need help

so I've never posted anything on here, this is all kinda new to me but I need some advice. I'm 17 years old and sexually active, a couple days ago I noticed a greenish, yellow bruise on my boob, near my nipple. and ik I haven't hit anything or I would've felt it. but it doesn't hurt. it's just there. and it's really scaring me bc it's bigger then a quarter. I looked it up on the Internet and all it said was something about my blood. I do have a blood disorder but why would it show up on my boob?? if it could be anything else or y'all have any responses at all plz help.