Suggest Treatment Painful Dark Bumps On The Buttocks With Dry Skin

hi doctor i have dark bumps on my butt for 3 or 4 years....some time i have pain and some times not...now my butt is looking so ugly with the dark marks..and also i have blacks marks on my body which i have no idea where it comes..my skin is so dry and my face is oily some place and some place its dry. i have small pimples all over my face which does not contain any liquid..