gas and tummy pain

My son is about three weeks old. He was in  the NICU for the first week. In the nicu he never had gas pains or problems feeding. He did spit up a little so they switched his formula from Similac pro Sensitive to Similac Pro Advance. Now that he's home he's having gas pains after every feeding and has at least 1-2 large spit ups per day. Should I change his formula again? I went to the pediatrician last Friday and really did not like her. He's not seeing his new pediatrician until Jan 12th - she's booked until then. What should I do? Is this normal?