What Causes Itchy Bumps On Penis Shaft After Sex?

Hi this last weekend me and my girlfriend had more sex than we usually do, and monday morning i woke up with a few bumps on my shaft by the head of my penis. They started off a little red now they are raised and they look like they have a black head inside them. They were itchy for a couple days, but now the irritation has limited down to just two bumps. I put Neosporin on them and covered them in a bandage because i thought they were irritated from my zipper on my pants. The black when away, now its just raised and they dont irritated anymore. Do you have any idea what they are? I know my girlfriend has no STD's or anything.