I Keep Getting Bumps That Are Either Painless Or Sore

I keep getting bumps that are either painless or sore on the scalp. Sometime they break and are fluid filled. I had a number of them around my hairline around my ears and back of the neck, a few on the top of my head or around the front hairline. I am using Selsun Blue 25% strength which works but never totally clears up. What is this?