Help - 3.10 year old potty training regression

[purpleshortcake]

I have a twin boy and girl who were 3 months premature. They started potty training around their third birthday. DS picked it up quickly although has always seemed to need to wee with much greater frequency. DD struggles with intermittent constipation which results in "skidding" but controlled with Movicol. She is now dry at night whilst DS is in pull ups at night. They are now 3.10

Until Easter they were at private nursery or with a childminder 3 days a week and me the other 4 and both were pretty much dry (maybe one accident a week). However since starting school nursery at Easter DS has really regressed and now has wet accidents most days at school and has starting having them at home / out and about too. At least daily, sometimes 5-6 times.

He takes himself to the toilet or potty a lot and alternates between sit down and stand up wee's. However he is not getting upset when he wets himself - unlike his parents.

It is so depressing as we thought we'd cracked it and nothing we try seems to be helping. We've not put him back in pull- ups (except for the odd very long car journey where he's likely to fall asleep). Is this normal, does anyone have any ideas?

Drowning here in piles of wet Dinosaur pants and jogging bottoms.....x