Sounds like my SO and I when it comes to the 'pick me ups.' I think one thing that helps me is that my boyfriend will almost kind of ...ignore me... if I start complaining. Or he'll tell me to go to sleep. Or that I'm not fat, dammit. It helps. Not at the time, no, because I feel resentful and angry. But afterwards, I feel better. Because really, I am kinda almost just wanting attention, and that's why I do it.
About the PDA, I TOTALLY understand. I think holding hands is perfectly fine. No one I know would look at a couple holding hands and not smile (or in my case, be sad because my SO is gone two weeks at a time). When it comes to hugs, that's fine too. You just gotta convince yourself of it. Little pecks or quick kisses don't really get people angry either. It's the nasty making out profusely and refusing to stop that people get grossed out by. Just tell yourself that, and work up the ladder of PDA. Just hold hands with him for awhile, despite your level of comfortability. It will come naturally after awhile.
And true, like the other girls said, you never HAVE to do it. But to me, it seems like you WANT to be able to show your affection. I might have misinterpreted it though. Good luck.
Sorry, I wrote a lot.
Oh, and edit: When it comes to getting dirty looks from older people, just glare on back. You (and they) should know that holding hands, hugging, or little kisses of affection are not ANYTHING to be ashamed of. (You can tell that I love snuggling in public if I'm just with my boyfriend. When we're out with his friends, I tend to be a little more distant though, because they have made it OBVIOUS they don't want to see that by hinting around that they DONT LIKE ME. And they're jealous because they don't have girlfriends...
)