My 6 month old does the same thing. He would take forever on a number 2 nipple and as soon as I switched to the number 3 he consumes it with in 7 to 10 minutes and I do not have a chance to burp him as well. I just get one big burp at the end. He also has reflux and we are on Enfamil AR, which is thicker, so he only sometimes spits up. But anyway, being that yours is only 2 months old, I would try to burp in the middle of the fed. Is she on any medicine for the reflux? If so, maybe she has finally started to help with the pain and is able to drink better!