Very awkward question

So..sometimes when I change my baby's diaper.. His penis is hard, which is whatever..but I've noticed that he tends to cry when it is hard. Like this morning he was scratching at his diaper and crying so I went to change him. His diaper wasn't very wet and when I put the new diaper on I put it on loosely because he was "up" and he seemed upset about it and it wasn't until it was down that he stopped crying. This isn't the first time I've noticed that he cries when it happens. I know it's a really weird question but has this happened with anyone else? Or should I talk to my doctor? Forgot to mention that he is circumcised which went smoothly and his penis looks very normal.