Weird smell from crouch

So I've been having a really foul smell coming from my crouch even after I wash it and I've gone to 3 diffeent gynecologists and they say that there's nothing wrong and even after I wash my crouch the smell is still there and the area of the towel I wipe woth comes back dark but the doctors say there's nothing wrong. Does anyone else have this problem or any ideas of what it is or how to stop it.