Is this behavior in my toddler normal body discovery?

Okay, my son will be three next month and we have been working on potty training for a while now and he is doing much better. A few months ago he discovered that his penis gets erect if he touches it, in the bathtub. He would say things like look mama, "It's long" or "It's big" or "It's hard." It freaked me out a little at first, but I know that its normal for a boy to discover himself. He is very smart, so he knows words like long and hard, even though I'll admit I was a little freaked out by him using a term like "hard." He wasn't stroking his penis in any time of adult way or simulating any strange masturbation or anything. Honestly, he is never around anyone in a daycare or any strangers. The only people who keep him when I'm not watching him are his dad or the same relatives that kept me and my sister and cousin growing up- and we had a normal childhood with no sexual abuse or anything. I'm not suggesting sexual abuse. (The thought does freak me out and make me paranoid, but I really don't think this is the case). I asked him if anybody touched his bottom and he said me, because I popped him on the butthole....LOL. I only barely popped his hiney def. not his butthole). Well, two weeks ago nearly, he had a misquito bite on the cheek of his butt and he scratched it a lot with me constantly reminding him that its not "nice' to scratch your butt infront of people and trying to help him understand there are germs there. Well, now, he has moved on to scratching his anus. I even had him show me where he scratched it and asked him if it itched and he said yes but I'm not sure if he understands and means it itches or if he just has a new obsession with rubbing or touching his anus esn't seem to be sticking his fingers in his anus, but then again, he does it mostly when his pullup is on, so I can't exactly see. I read online that he could have pin worms. I thought about getting medicine incase. I even thought that it might be a habit and that I could put overalls on him, but that will interfere with potty training. Have any of you parents experienced your child as a toddler being fascinated with touching their bottoms or thier anus? Should I be worried?