I have just noticed that you have *just* given birth to a new baby. Often children will regress with their toileting when a new baby comes along, very very common. Perhaps he doesnt want to go back to wearing a nappy because he is a 'big boy'?

Keep a mop and bucket handy and keep reminding him to go to the toilet.

Perhaps some 'special undies' like with his favourite character on it ..may encourage him to go to the loo?

It may be his way of getting your attention with the new baby this behavious is extremly common in toddlers with new babies. So perhaps, as hard as it is, try spend some special time with him without the baby?

HTH
Jen