Is this upon ejaculation or during intercourse. This article is helpful going through lower abdominal pain for males. It starts with females but then continues on to common reasons men have the type of pain you describe. I know you said kidney but that's just an area you are guessing. You have no issue when urinating, correct? If you did, that would more likely be a kidney issue. Here is the article you can copy and paste: https://www.healthline.com/health/lower-abdominal-pain-during-sex#in-males I think you should see your doctor. One common cause is prostatitis. This sits just below the bladder but can have the symptom of lower abdominal and back pain (probably where you think your kidneys are). Anything else going on to add to the symptoms. Get checked by your doctor and let everyone here know what they say, I'll be interested.