Question: have red bumps on my penis

Hello, thank you for your reply. I want to give you a detailed story so u have allthe facts about my situation. I am 35 year old male, I have had an active sex life for the last 20 years and have had a few dozen partners in that time. About 3 months ago i met my current g-friend, and after our first intercourse i found a few small red spots on my penis on the head and under right where it meets the skin and even on the inside of the skln. I felt no pain or itchiness, just slight discomfort and a feeling of burning when i peed. I was worried it might be some STD, so my gfriend and i went and got tested and both tests came back negative on everything. The red spots went away few days later and i didnt think much of it. I didnt see her for about a month and didnt masturbate in between. When we had sex again, i got the same reaction of red spots slight burning and discomfort, this time i used some topical cream and the spots went away the next day and the discomfort the day after. I thought that it might be what happens when her and i have sex, maybe our bodies just dont react well, but then about 2 weeks later i had the same reaction to just masturbation when i was by myself about 2 weeks after my last intercourse with her. Now its been about a month sinse ive seen her and still have the same reaction every time i masturbate. I have never had this reaction to sex or masturbation, i know its not a STD because i got tested for all of them, but im wondering if i could have gotten some other type of infection or something that is now making me react this way to masturbation. thank you