You should try meditating, it's done absolute wonders for me, and I haven't even really come any where near being able to meditate deeply yet. There's plenty of vids on youtube to give you an idea of what it's about and how to do it. There's also plenty of books that can help you immensely. I very much recommend power of the now, which I am reading at the moment. I've read a couple of self help books and whilst they have a reputation for being cheesy when you're suffering from depression they can really uplift your mood and put some perspective on things.

Or you could ask for professional help, though it sounds like you're just suffering the blues rather than having any clinical problems. It sounds as though you have your mind on particular things in your life at the moment that are causing you to feel down, which is not much of a problem really, although it can feel as if its the biggest problem in the world. Certainly getting out and meeting new people will help. You really just need to be able to get your mind past these things that are getting you down, and come to the realisation that the fact that you should be enjoying your precious time on this planet is infinitely more important than the fact that you got dumped by some girl, or whether or not so and so likes you. You should be the most important person in the world. More important than any celebrity or political leader. You control the world that you live in, not anyone else! You need to take your world by the balls and give it a good slap in the face!

Also, try not taking things too seriously. When something embarrassing or shitty happens to me I tend to just usually laugh about it. For example, now I think getting blown out by a girl in a supermarket full of people is fucking hilarious! I literally walk away pissing myself, and so do most people standing around. This is just an example of the type of mentality that you need to get through life. I'm not gonna start banging on about how hard life can be, because I'm sure you're aware of this fact. However, if you're going to make it to a half decent place in your life then you need to be able to think past through the trivial shite, and say "well this is shit, but hey that's life" and just carry on through. Anyone that is unable to do this will lead a very miserable existence.