Hello. I Had Sores That Developed Out Of Nowhere All

Hello. I had sores that developed out of nowhere all over my penis, which were a bit painful. I did have a cut on my penis from rough sex with my gf. Since then I have had rashes and little tiny blisters or pimples that develop.. usually its a red area with like a couple of blisters or pimples. I have been with my gf for 5 years and she is the only person I have ever slept with. This has been going on for about 2 years. My girlfriend has not had any of these symptoms happen to her. What could this be? an STD? or something else?

Thanks