What Causes Red Bumps All Over Body?

Hi i was looking for some answers on my skin rash.. it started out with red bumps on my stomach kinda looked like lil pimples but they didnt form whiteheads and then it spreaded to my arms and legs and some are on my face now and even in my scalp.. at first they didnt itch but now they are beginning too .. i have been to a dermatologist once and he gave me some topical cream to try but it has not cleared it up yet.