What's wrong with me? ?

In High School I was always on top of game. I was always the cheery happy guy that everyone got along with. Then things changed I became infatuated with this girl. She was on my mind 24/7, anything I did, I had her on my mind. Turns out she wasn't interested in me. Depression hit me like a car on the freeway, and Id cry myself to sleep. No matter wht anybody told me I couldn't get over it. It got so bad I couldn't socialize, and I dropped out of school. Its been 2 years and things just keep getting worse. I cant go out in public without feeling like everyones looking at me. I'm 19 and I look like I'm in my mid twenties, When people talk to me I flinch, I cant look at them without feeling nervous "even around my own family". I have no motivation , I cannot leave the house willingly. Please help I need Psychological advice, Im sick :*(