I have issues concerning my appearance?

Basically, i have a serious issue with my self-esteem and especially how i look. I've never really thought hard about it until recently but the thing is i have some serious issues and i want to know how to deal with them... I avoid my reflection everywhere except for the mirrors in my house and a few in other peoples houses and thats it!? And i wont look in a mirror if there is someone else being reflected too, and i wont look in the mirrors in school, in toilets, in strangers houses... And i don't just avoid mirrors; i avoid glancing in windows, doors, and recently even shadowy reflections in tiles and saucepans, like seriously wtf? I actually sub-conciously avoid looking at reflections because when i do i just see faults and i become really sad and usually angry. I hate pictures and videos, i literally never let anyone take photos of me and hate any pictures i do take. I feel like what if i am just one of those people who aren;t good looking? Like they exist, and it doesnt make them a bad person or anything, they just aren't pretty... Is that me? I've never told anyone this,i'm too embarassed. I mean, i've been like this for 3 years maybe... and i'm 17. Please; any advice? What do I do? I'm sick of this insecurity.