Painful erection 8 hours after one ejaculation

[dickhurts]

Erection and ejaculation is perfectly normal, everything goes well and without pain. However, if I get an erection afterwards, the whole muscle hurts and more towards the upper part. I can pee perfectly fine, however. After around 8 hours it goes back to normal. It's always been like this. I have never seen blood or anything strange. Pain intensity won't change if I leave days apart or do it days in a row or if I use lubes. And I don't treat my "boy" harshly.

Some background: 18, virgin, skinny and in a healthy condition, both mentally and physically.