A dark grayish slightly bumped less sensitive skin with grainy texture. what is it?

[ntyetready]

Hi, im 29 years old. I have this skin condition for a very long time, probably from my puberty or before that, about 15 years as far as i can remember. Its on my right shoulder. A dark grayish slightly bumped less sensitive skin with grainy texture. Granule like things comes out. If i stay in the sun for long it gets sensitive, pimple like things shows up and bleeds with usual pain. Its about 5 inches in length and 6 inches width.  I showed it to a doctor in Thailand, Bumrungrad Hospital about 10 years ago and he said its  becker's nevus but when I checked it after in the internet , well its completely different than the one I have on my shoulder. I dont know what it is and in my country doctors are less reliable unfortunately. Can anyone please help me out some way?