Here’s an option: Accept yourself for who you are.
I know that sounds trite, but nothing you’ve mentioned is any sort of great moral or personal failing. If you’re the guy who thinks too much, be the guy who thinks too much. There’s worse things to be, man. God knows, it’s not like the world has an oversupply of thinkers.
The two specific things you’ve mentioned are sleep and social situations. For the former I’d recommend following Anaamika and Mr. Bus Guy’s advice. Especially Anaamika’s. Not that I’ve ever tried it myself of course. No sir. But I’ve read in books that it works. Yup, books. That’s my story and I’m sticking to it.
For the latter, I’m not sure how bad the situation is. A few ideas.
Again, one thing is to learn to live with it. You may be better in one on one conversations than in large groups. try and associate with like minded people. Find a few close friends, rather than trying to be the life of the party. Don’t fight your personality, embrace it. The problem with fighting your personality is that it turns into one of those “don’t think of an elephant” things. The more you try not to think of an elephant, the more you think of elephants. If you try and suppress overthinking, you’ll wind up overthinking about overthinking, if you catch my drift. If you embrace your overthinking, you may find it becoming less of a burden. Sounds paradoxical, but it’s true.
Mr. Bus Guy may have been kidding when he mentioned strong drink, but there’s nothing wrong with moderate alchohol consumption in social situations. It doesn’t have to rise to the level of a liquid lobotomy. One or two drinks will lower social inhibitions without turning you into a full on drunk. I mention this merely as an option. I don’t know how you handle alchohol.
Finally, if you really feel like you are experiencing severe anxiety in social situations you could always see a doctor about it. There are several anti-anxiety meds on the market. One caveat, and I know I may sound a bit Cruisey here, but Doctors perscribe these meds at the drop of a hat now. Ask yourself if they’re something you really need. If they are, though, then go for it.
Hope this helps.