Bothersome nappy

[WJM2020]

Hi all. FTM so every time something new happens if I haven't seen it before I'm like 😳😳😳😳🤷‍♀️🤷‍♀️🤷‍♀️🤷‍♀️🧐🧐🧐🧐
Anyway, the last two days my 18mo DS has been pulling at his nappy. Usually I'd take it as a sign it needs changing but he does it even when a fresh one has gone on. He looks quite pained in the face too and whinges when he's touching (touches the back and sides)/pulling it.
He does have a slight nappy rash atm but he's had a lot worse and it's never bothered him.
He isn't ready to potty train yet so it's not that either.
Any thoughts as to why this new 'thing' has come about?
TIA

It's been ages since I've had a small child but before potty training, there was a stage where they liked taking off their nappy because they could iyswim. For a while it stopped because I put them in dungarees and sleeping bag at bedtime but they eventually worked out how to get out of those too 🤦🏻‍♀️

Oh dear @cherryonthecakes 🙈
Well a few hours after I posted he bust out in a rash down his legs, blisters on his hands feet and in his mouth, it was Hand Foot and Mouth for the third time 😩😩

My ds went through that stage and I used bodysuits which prevented it happening. I used to put cream around his waist as well if that was irritating it but it wasn't the case. I think he just wanted to be naked but he wasn't toilet trained at that age.