Are there any books that can help me/DH explain this in terms he will understand?

This morning the poor little thing said 'i feel strange mummy' I asked what kind of strange (actually thinking his sore throat got worse), and he said 'behind my willy feels really odd', then proceeded to sit on toilet for a poop and screamed it did subside very quickly, and he thinks his need to poo caused it. (His words to me, I didn't tell him that)

I have noticed he has had an erection in his sleep before, but it has always gone down before he has woken, so as far as I am aware, it hasn't worried him in the past..

DH is very technical in things, and has trouble explaining things in a simple term and amount kids need to know, so really need help on how to explain this..