If what you're seeing looks like a symmetrical swelling near the base of his penis, near the scrotum, what you see is probably the bulbus glandis, the part that swells during mating that causes the dogs to 'lock' together. It fills with blood and swells when the dog is excited, even in a neutered dog.
May 13, · My dog gets pus filled pimples on the outer part of his penis. Solution: If these bumps are occurring in a small localized area you can try giving benadryl (generic is fine). The usual dose is 1 - 25 mg capsule for a dog over 25 lbs times a day. If the condition and/or itching does not improve after days it's time to see a vet.
If your dogs are not itching or licking the affected area then it means that these red bumps are no causing any problems. It is normal for the dogs of 6 months to 1 year age dogs to have pimples. These might be simply pimples. These are like acne in young boys and girls.