I don't know whats wrong with me

Sometimes I just genuienly don't feel real. Whenever I'm spending time with friends and loved ones and my partner i feel normal, or at least as normal as I can seem to feel. But the second I get alone with myself I just feel worthless. I start craving attention from anyone, anything to make myself convinced im worth someones time. It's as if i cant feel anything and im feeling everything at once. I think I've been depressed for so many years of my life that I don't know anything else. I just wish I could be normal and happy. I mean, I have friends, and a relationship, and a roof over my head, and I get good grades. I'm captain of my sports team. I should be happy, I'm just not. I want to be though. Any words of wisdom?