http://www.med.nyu.edu/psych/screens/depres.html
You sound like you would benifit from treatment. The part where you say nothing sems good or fun is the part that worries me. That can indicate a chemical imbalance (actual medical depression) where your ability to feel pleasure is reduced. This can be fixed with medication, and will give you the ability to heal; however, it won't work without counseling and attitude adjustment. Medication gives you the strength to do what you need to do, but the decision to do it comes from you.
Negativity is a personality or attitude, but it will predispose you to depression because it makes it difficult to get out and do things--you are always sure it won't work, and when it does, you're sure it's a fluke. It might be worth your while to practise good mental habits where you train your mind to find one good thing about every event or situation.
My Yogi used to say that the human brain had three decison-making bodies: the negative, positive, and neutral. He said it took 3 seconds for a thought to progress through. That means most people's knee-jerk reaction (less than 3 seconds) will be negative. Spending more time thinking before saying "no" will enable your positive mind to inform you of potential good things. He used to say everyone should take 10 seconds to make a decision so that all 3 minds have their say. Even if this is just hocus-pocus, giving yourself extra time to think and making a point of ALWAYS seeing bad AND good is a healthy mental habit and vital to your well-being and ability to make sound decisions.
Good luck!