HELP. I had this forever and can't rid of it

This messes with my self confidence. I can't where a nice bathing suit in piece.. I swear I tried everything even Clorox. I try to even cover it with make up and it still doesn't work... I changed my posture and I'm constantly trying to sit up.. but please help me. My cousin told me I would have to get pregnant in order for it to go away but I'm 16 I had this since the age 12 pleas help.