Please help if you can!

My little boy is 7 1/2 months old. He’s been battling reflux since he was a little over one month old. He’s tried several meds and several formulas. Last Tuesday he finally went to the G. I. The dr. decided to keep him on his same meds. (Prevacid Solutab 15 mg. twice a day, Beth…?? 0.8 ml four times a day, and Caraphate 1.0 ml as needed.) The dr. changed his formaul to Similac Alimentum to see if maybe he has a milk intolerance. After a few days I thought the formula was working because he wasn’t spitting up as bad and he wasn’t as cranky. I know that I should give the new formula at least a month, but my question is he now has a horrible rash under his lower lip, on his cheek, and on his back. This rash just started since he started the formula. It’s red and raised looking. Today he cried all day long! We go to the G. I. again next Friday. I’m at a loss as to tell him how things are going. He is now spitting up A LOT…it seems like more than before. I am so frustrated! My little boy is so sweet and loving. I just want him to feel better, but I don’t know how to help. Do you have any suggestions?