Dark brown skin between legs, how do i get rid of it?

I have darker skin around my groin... but not anywhere else! is this because my legs rub together, because i'm not skinny, but i don't have anything on my neck, under my breasts, or my under arms. i'm fairly young to ask ym mom to take me to a gynecologist, i'm 15, and i don't want it to be diabetes! i just can't seem to lose the weight! i exfoliate, and nothing seems to work. i can't get a perscription, because of what i just stated before. please help? that'd be great. i feel so self concious. especially when i get older, i don't want to be sexually active, and have my husband think i don't clean myself!! because i do! :O please help me!

I am 13 and i have had the darkness in my thighs and slightly under my arms and neck since i was seven or eight . i have used a loofah sponge i have used cream , i have even used toothpaste and i have yet to see results. my neck has cleared alone and my underarms have also cleared. i know really did anything under my arms or on my neck , i only focus on my thighs. although i feel a little insecure in my ballet school on my first day girls laughed at me but it didnt really bother me and i still shamelessly spread apart my legs, but when i get older i do not want a boyfreind or husband to see me in shorts.