Introduced formula...

Let me start by saying that he has an appointment with his pediatrician today. Anyway, my son has been exclusively breastfed for 5 months now. I am getting ready to go back to work (wasn't planning to go back but some things came up). I do not take well to a pump. I've tried three different types and I just don't get much so trying to work 60 hours a week and pump when I barely get anything is just not going to work. So, last week i started weaning. I started by giving him 2 bottles a day. Well, I noticed his cheeks and around his mouth got red but it went away quickly. Now he's on 5 bottles per day and while he's drinking his face, chest and under his chin are getting red and today he broke out in little gives on his chest. Any ideas? He's in Similac sensitive. I'm pretty stressed because I start my job in a few days, my milk is drying up and idk what to do :(