Is it okay to think I'm pretty?

Ok so when I used to think I was pretty and I was really confident and happy. But one day I just didn't see myself like that anymore because one of my siblings said I look horrible.. but I looked in the mirror and thought maybe I wasn't that pretty after all..Then later on i thought I was buying into it to much. It seems when I finally admit to myself that i think i'm pretty I suddenly start to feel ugly because i'm brought down. There was this girl that called me ugly and then I thought I was for a little bit but some people reasured me she was just trying to get to me. Most people say I'm really pretty but some times other girls say I'm not and call me stuck up but i'm not.. Does that mean it's wrong to think I'm pretty? Is it stuck up in any way? I feel so much better when i'm ocnfident with how I look but now I'm afraid to be confident at all in any way.