Hi Shauk! Nice pics, you are a hottie (really!).
If you want to keep the weight off, you'll have to change your lifestyle. Eating healthy, moving more, you know. It'll keep you fit and possibly extend your life or at least decrease your risk for stuff like diabetes and high blood pressure. Plus, it's a long-term plan you can stick with til you're dead.
Anyway, this is what I advise (and take everything as slowly as you need)...
DIET...
1. EAT A GOOD BREAKFAST. This will kick start your metabolism. It should have complex carbs (muesli is fine, Squarepants cereal is NOT; steel cut oats over instant oatmeal), some protein (melty cheese toast, eggs), and fruit/veg (green pepper and onion omelette). I've heard that green tea can boost your metabolism, too, and I'd recommend it over coffee. I'm also gonna recommend replacing artificial sweeteners with honey. Honey's got a flavor all its own and it has some antioxidants whereas sugar has none. Try to get it as unadulterated as possible (in general, treat your food like a potential sex partner - the more it's been around the block, the less inclined you should be to errr... put it in you).
1a. Get a fridge and start making meals at home. I think the Zone diet has a pretty good guide to what proportions of what you should put into your body (it's a pain to measure everything but you can kind of get the idea). You get protein, all the veg you want, tons of fruit, grains, and a little fat. But I also think ideal diet varies person to person (e.g. some people can take more meat) so you'll have to experiment.
1b. Stay away from processed foods (that includes Taco Bell and diet soda) only because most is junk and the food in there is mostly stripped of nutrients. I like cheese though and I think it's just fine cuz you can get low-fat kinds (travesty!) or get some good pecarino/parm (NOT the green shaky can!) and just shave a little bit on your scrambled eggs for flavor. You want to eat stuff your body can use. Forget diet food (Special K, diet soda, Luna Bars) and forget those big iceberg lettuce salads that are drowned in dressing (iceberg has little nutritional value anyway - opt for spinach). Throw out the white bread and forget whole wheat bread (just a little bit healthier than white). Get some pumpernickel or rye - stuff that feels chunky in your mouth and not like wimpy fluff. Brown rice over white rice, lean meat, frozen veg over canned if you can't get fresh.
2. Stop drinking soda and JUICE. Juice is high-cal. Just stick to water. If you get bored with water, you can flavor it with some lemon, lime, orange slices or cucumber. Don't buy that flavored water stuff if you can avoid it - do it yourself. The above posters are right about diet soda - it feeds your sweet tooth and trains it to crave refined sugar, not natural sugar from fruit. If you drink milk, switch to skim or soy.
3. Keep fresh fruit and veg (celery and peanut butter or chopped peppers and hummus) on hand for snacking and to round out a meal. It really makes a difference when you cut out junk food AND you'll be getting a lot more vitamins & minerals. I personally think this is more healthy than power bars (also cuz power bars leave me hungry - I have to eat like, three!).
4. Prioritize nutritional value over calories. 200 cal of fruit is healthier than 100 cal of Weight Watcher's cookies.
5. You know... it seems like you have the time to take up cooking as a hobby...

You might dig it! Ah yes, you can cook in a microwave if you don't have a stove. You can also get a rice cooker that doubles as a steamer to do some steamed vegetables and fish... and rice. If you do take up cooking, look into different ethnic cuisines - the American diet is ridiculous.
EXERCISE
1. Nice advice on the interval jogging from a poster already. I eased into running by lap swimming, actually. It's fun to be in the water and you can go at your own pace - it's also a low-impact, full body workout and burns just a little less than running if you're swimming hard. The only thing that sucks is you have to have a pool membership.
2. Just start moving more. Take a walk after dinner EVERY NIGHT. Take up tennis or basketball with a buddy. Take stairs instead of an elevator.
3. Gym memberships can be pricey but spring for one if you will use it. I never used mine enough to justify the monthly fee. I love the fact that you can go running anywhere at anytime (mostly). Anyway, if you want a gym membership, sometimes the big ones will do a month promotion where they'll discount or waive the horrendously large initial signers fee - check the net.
4. Buy yourself some workout gear if that will help motivate you.
5. Set up a routine that you can fit into your schedule. I do a morning or evening jog at least 3 times a week interspersed with pilates/yoga/weights on the other days. The muscle you build from weight training will burn more fat but the cardio is key to really reducing it. Generally, I think it's recommended to do cardio 3 times a week for 30 minutes at least.... But see how much you want to push yourself.
6. On running... Take it slow, walk when you need to and push yourself when you want to. Invest in a good pair of running shoes (used ONLY for running) and an iPod if that'll help. Stretch before and after (run with warm muscles). I used to hate running and sometimes I still head out the door reluctantly but there's nothing that compares to the feeling of running like a wild horse in the field. Idyllic, but true. You really feel the physical strength and abilities of your body. It's GRRRREAT!!!!
THE MOST IMPORTANTLY...
1. DO NOT OBSESS ABOUT YOUR WEIGHT ON THE SCALES!!! You will put on weight if you're building muscle (esp. cuz you're a guy) and you'll see the change more in your how your pants fit than on the scale. You can definitely lose a lot in a few weeks but it's a commitment to a total lifestyle change. The last thing you want to do is get on a yo-yo diet where you cut calories and gain them back later because diet food sucks.
Anyway, hope some of that helped - that's been my experience at least. Good luck, wish I could cook you some dinner in person! Oh, and keep us posted on your progress!!! Btw, I think there's some sit-up group effort here on TFP... and a distance as well. Post your numbers!
EDIT...
On your loss of appetite... damn boy, put away those cookies!!!! Get yo'self an APPLE! Even if it's oatmeal raisin.
A decrease in appetite is a side effect of a healthier diet. Better food with more fiber, complex carbs, etc. will stay with you longer than a sugar fix. Exercise will also decrease your appetite. Basically, getting your body into shape will make you more aware of how much and when you need to eat and you will also get the urge to work out.
But it sounds to me like your loss of appetite is temporary (like you were just not hungry one day) - don't rely on that for weight loss but don't eat more than you feel you need to. Eat breakfast and whatever you need to get through your day (and your daily exercise) but stop eating those cookies!
Here are a few websites (the Zone can be hard to follow but use it as a loose guideline)...
http://www.wildoats.com/u/Health/superfood_foods/
http://www.enterthezonediet.com/