Hi Dr, I recently had a few rigorous sessions of masturbation and the next day I had a number of clear-top pimples on the shaft of my penis where it is most exposed to rub during masturbation. The area under the pimples seems to be swollen and hard and slightly red. I have had it a number of times over the past few years, always after rigorous masturbation or sexual activity. The pimples are quite sore and sometimes i experience swelling in the glands in my groin. I tried popping them once and it was really painful and the glands in my groin swelled up quite a lot. Any idea what this could be? Ive had STI checks done recently and all came back negative.