This is really nothing to do with periods or health in that way but I'm 13 and I think I'm an okay size for my age as I am 5'1" and I weigh 95 lbs. I play volleyball and wear spandex and I started to notice lines by my bum. usually a person only has a line which is where their butt ends but there are multiple smaller lines and I know they aren't stretch marks. they're only on my left lower bum. my butt checks seem to be uneven in size??? how do I even them out and get rid of the lines?