It is unfortunate that you stopped your son’s pre-k attendance at precisely the time he was likely to feel the emotional pressure created by the presence of a new baby. If he enjoyed his school, had friends there and was learning new things, his sudden withdrawal from the program is probably quite frustrating to him. That, plus the new baby and the increased time demands placed on you, means that his daily life may not seem as rewarding to him as it did previously. He is compensating by demanding more of your time and attention—and love.
One thing I would do is find as many informal play opportunities in your neighborhood as you can. Also, try to involve him in the care of the baby to some extent. This will help him realize how much time the new baby requires and enable him gradually to understand why you cannot spend the entire day playing with him. In addition I would find a “special time” during the day for one-on-one interaction with him. Inasmuch as it is possible, let him choose the activity for that special period. Make sure the baby is asleep during his special time so that there won’t be any competition for your attention. And make sure you do a few “babyish” things with him occasionally—hold him on your lap and rock him, snuggle against him when you read to him, etc. Finally, be sure to find opportunities to compliment him on being a “big boy,” and tell him it is a big relief not to have two babies in the family.
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.