Toilet training regression...

I really need some advice please.

My DS is 3 and a half and has recently regressed with his toilet training. He's fine with poo but terrible with wee.

If we are at home he will leave it til the last second to go to the toilet and will have already started going by the time he gets there so there are always wet undies and often drops of wee all over the toilet floor.

Every day at kindy he comes home in changed clothes from wetting himself.

Today I took him to chipmunks playland and even though I asked him repeatedly if he needed the toilet he fully wet himself twice!!! He didn't even tell me he just kept playing with wet shorts! I just couldn't believe it! He's obviously having so much fun that he can't be bothered to stop to go to the toilet. The same must be what's happening at kindy, just too busy to bother???

Should I come down hard on him for this? Should I punish him for wetting himself or should I perhaps reward him for going to the toilet? I was thinking maybe a snake lolly or marshmallow for every time he goes to the loo successfully with dry undies?   My DH isn't so keen on this as we know its not ideal to reward kids with food. But Im desperate! We were doing a gold star chart but obviously he's not worried about that anymore because its not working!

As a nurse it has crossed my mind that he may have a bladder infection and that's why the urgency but this has been going on and gradually getting worse for a couple of months now and his urine isn't smelly or cloudy and he isn't unwell in any way.

He's been toilet trained for ages now so I really need to sort this out. Any advice greatly appreciated. Thanks.

One thing you could find out is if it hurts to pee. Sometimes children develop a urinary tract infection and hold on until they wet themselves because it hurts to wee. Does he complain at all of it hurting when he pees? You could get it tested at the Dr's.