I'm probably the last guy who should attempt to help, as I've always been confident, verging on cocky (sometimes obnoxiously so). But I'm so awesome, I think I can help you anyway, lol...
The only supp I can think of that might help, and is affordable enough to take everyday, is DHEA. But at your age, I doubt you need any. But it wouldn't hurt to buy a small bottle, and dose it maybe 50mg ED in the morning, just to see if it helps.
If you end up trying some prescription anti-depressants, I'd recommend Paxil. My ex-GF was seriously bi-polar, and Paxil worked great for her (when she actually took it). It didn't turn her into an emotionless zombie; it merely "took the edge off" of her moodiness. (Do you even have the "manic" part, or are you simply depressed?)
Beyond the chemistry, I really have to agree with MOHAWKA. Find
something that you're truly passionate about (for me, it's mountaineering), and throw yourself into it. As you begin to excel at it, your confidence
will grow. And it will simply make you happy; you'll feel good.
I also want to agree with BigNutz (appropriate name, lol) about hooking up with some girls.
Nothing makes a guy feel more confident than banging chicks. (Except maybe kicking some ass in a bar fight, but I
don't recommend that, lol.) And the cool thing about getting laid is, it gives you exactly the kind of confidence that girls find attractive. So it becomes progressively easier to get the second girl; and then the third; fourth, etc... And it's perfectly OK if that first girl isn't exactly Alba -- they
will become better-looking as you improve your skillz. And guess what? You'll eventually find one that you won't want to discard -- you'll actually like her, lol. When you find that girl, and have a long-term, fulfilling relationship, all the confidence you've been gradually building will mature into peaceful self-assuredness. You'll
know you're a decent guy with passionate hobbies, and interesting stories to tell.
So...
Step 1. Buy some cheap DHEA.
Step 2. Find a hobby that will take your mind off of how crappy everything is.
Step 3. Seduce some average-looking girl. (And wrap your junk, duh.)
That's really all you need -- 3 simple steps that will forever change your life. You're welcome. (I should write a book.)
-J2x out.
[EDIT: I just saw KSMA reference some "post about your wife," but I can't find that. So I'm not sure how applicable my babe-banging advice is? Too bad -- that was my strongest stuff.]