Potty training - night time poos. Help?

Anyone had similar or can offer advice as to whether there is something
we can do?

Our little one, 2y 3m, decided he didnt want to wear nappies anymore (I
was hoping for summer training but he had other ideas!) and it has gone
ridiculously well with no accidents in 3 weeks. He wears pants in the
day and nappy at night. His nighttime nappies are mostly dry as he is
waking up in the night and asking to use potty/ toilet. No problem
there. Im very impressed. We have been rewarding a wee with a sticker
and poo with a sweet.

However, the last couple of nights, after he has gone to bed he has
ended up asking to sit on potty and is doing lots of poo over a period
of 2 hours. Our problem had been the sweet thing, so he has been doing
a bit, getting sweet, then saying his tummy still hurts so does
another. Soem of these poos are tiny This goes on forever and means our
evening has gone. We will of course rethink the sweet and maybe say he
gets one sweet in the morning as its past bedtime. Last night was a new
one though when after this evening escapade he was up at 3 for an hour
to do more poo - he only did one but kept saying he needed more.

He is still in a cot so we are up to get him out and on potty. We then
turn the light down very low, give him a few books and leave the room
so its not as if he sees it as playtime.

With a 4month old too who is going through a funny night waking and
being wide awake wanting to play phase we are slowly being driven mad
through the usual sleep deprivation that we all know so well.

Sorry to ramble on but I would like to know your ideas/ advice/
stories.
Beccie