I'm really lonely and sad all the time?

I have friends, but sometimes I feel like they don't care much about me. They hardly invite me and i'm always left out. Even when I have fun, as soon as I come home I just get lonely and end up crying. I'm jealous of my friend who gets a lot of attention, a lot of people like her and she always has a boyfriend. I'm not the kind of person people like. I hardly get noticed and I feel more comfortable staying quiet because I feel annoying. Guys don't like me and I just feel ugly. I'm just so let down and ignored that it is hard to be happy anymore. It makes me overthink things and i've become so sensitive. I hate being so lonely and the way i get angry at my best friend for being well liked. I just feel like i'm wasting my life being sad but it's hard to stay positive when nothing good ever happens to me. What should I do?