I don't know much about what you are asking except to say a lot of little children (boys and girls) masturbate. People write in on this site mentioning things like their child in diapers rubbing on the strap of her carseat, meaning, it happens quite young. And I don't suppose it happens in response to being molested, kids just sometimes find that area and rub on it or with it. If you were an anxious kid, you probably liked the feeling as a stress reliever.
Although I agree with previous comment, sexual arousal at such a young age, and moreover - having sexual fetishes like.peeing or watching someone pee tend to have their own triggers. Children who avidly masturbate without knowing it is a private thing, and something you don't do in front of the others usually have suffered abuse in the past. If you've seen documentary "the child of rage" which is about a girl who has suffered sexual abuse at extremely young age you might find similarities: masturbating til she hurt her private parts, sexually abusing her younger brother...naming a few. Although she had memories of being assaulted and molested. I don't see the same in you.
Go get IFS therapy. You've got work to do.