Suggest Treatment For Heat Rash On Body

After the birth of my first son, I have seem to be developing what looks like heat rash. On one day I will be itchy on the back of my neck. White bumps form from where I itch and if I scratch enough they bleed. When I wake the next day they are gone only to be itchy somewhere else like my back or legs or back of my hands. Today I couldn't stand the itching anymore so I took a benadryl. It stopped the itching, but now approximately 6 hours later, I noticed at the top of my buttocks are two circular shaped welts (on each buttock). They are hard, but very itchy. Should I take another benadryl?