How do i get rid of these dark spots on my chest & stomach?

Its been like this for a really long time now, about 2 years. Its an ugly sight & keeps me from ever showing my stomach, at all. its really disgusting and I want if G O N E. Please give me some advice to get rid of it. I thought maybe it was dirt, but i scrub it every time i take a shower, which is pretty much everyday, & it does not come off. It doesn't help. Please help me out, i really need some help, its so gross. Thank you <3