R.O.
I agree with the other posters that this maybe somewhat caused by attention seeking, especially if this means he needs more help from you. But beyond that he is having to adjust in a lot of different ways to having a new baby in the house. From what I hear other moms say, many times when a child is making progress in one area, as your son is having to with the new role of "big brother," they slip in other areas you thought they were past. I'm sure this doesn't help in any concrete way, but hopefully it is just a matter of time. Good luck!