The same thing happens to me an a whole bunch of other people out there. I get erections at the sight of diapers and putting them on as well as wetting them.
Diapers are huge sex turn on for me. You're not alone and are what is referred to as a DL diaper lover.
There's nothing we can do to stop getting these erections and loving diapers and I used to hate having these diaper lover feelings and I've now learned to accept it.