I'm such a terrible person

I honestly don't know how to stop feeling this way, it doesn't help that I'm sick and my best friend did something extremely mean that had zero explanation. It really doesn't matter if I do bad or good I just feel so different from everyone. When I was a lot younger I always felt as if I looked very different from everyone, I didn't know why, but even at around the age of 7 I started to feel like I was terrible. I wasn't a bad kid, I didn't ever get in "big" trouble. Even now with my group of friends or around people I know or don't, I just feel different. Most friends tell me "I'm just human" or "it's completely normal" but it never feels that way.

The worst of this is even when I get to be happy or in enjoying myself, one very small shred of awful feeling can drag me right back. I know that sounds like a "man up" scenario. I do try my best to just go through the pain, rarely it works.

Side note: I'm sorry if my grammar was bad or my post doesn't make sense, I'm currently sick, but I felt like I needed to just let this out.