D.Z.
M.,
Don't start cereal yet. Babies' digestive systems are not ready for solids yet at 3 months. 6 months is the earliest you should start, but some would say you should wait until one year or later. Offer bottles more often. My first baby nursed every 2 hours for his first 5 months, then went to every 3 hours for 3 months, then gradually decreased feedings from there. Your baby does not need cereal. He needs formula or breastmilk, especially since he was a preemie. Please don't stress out his digestive system just yet!
Not that you were asking, but I might also suggest that you not start him off with cereals when you do start solids. I have 5 children and the first 4 all started with cereals and then went through an awful period of only eating carbs (cereals, crackers, breads)...so my last baby I started on bananas and avacados, and introduced cereals much later, after she had tried every kind of vegetable and fruit I could get in her. She is 15 months now and eats everything,not just carbs. The younger Dr. Sears has a book that discusses this idea. I saw it on Dr. Phil or Oprah, can't remember which, but it worked. Just an idea.