I can't handle adult relationships.

Hi. I'm 21 and I haven't dated anyone in over a year, or had a serious relationship in almost 2. Which I know is fine. I don't mind it. I get lonely sometimes, but I don't know why I can't do relationships anymore. I dated the same guy from age 15-19. I lost my virginity at 16. I got over him a while ago so I know that's not what's holding me back. I just...I can't bring myself to date. I went on a few dates with one guy about a year ago and that's been the only guy I've "dated" since. Sex is also a tricky subject for me. I had oral sex with the second guy but I couldn't go all the way. So I haven't had sex in 2 years. Everything about dating and sex makes me uncomfortable now. I don't even remember who that girl was who loved it all so much years ago. Now I'm woman who couldn't even fathom getting intimate with someone because I don't really believe I'll ever be that comfortable again. People tell me to get out there all the time but it just gives me so much anxiety. I'm so uncomfortable. I don't know how I got this way. I thought dating was supposed to be a fun thing at my age.