I have stretch marks on my butt?

i dont know why they are there, and the bother me i dont have a big butt (never have, never will, hopefully), i work out daily, i'm not a fat person 5'2 84.lbs, when i swin the sort of show and it makes me insecure (more insecure than i already am.) and i i just want to get rid of them howww? :c >.<