18 month old getting erections

So this is so weird but I am hoping it’s normal.

I know erections in toddlers happen, but my son has them every single night.

He falls asleep on the couch every night ( I know, bad habit) and before I bring him in his crib, I change his diaper. He is always asleep during this time, and always, always has a boner.

I want to ask the doctor about this, because I feel like every night is excessive, but I feel weird explaining it to the receptionist, (I don’t know why) who relays the message to the doctor

Does anyone else know if this is normal???