I've always burped my two when they were little by sitting them on my lap, and placing one hand under their chin, and the other one on their back so they're say completely upright. My midwives have said this is a good way to burp, and thumping often breaks up the bubbles and makes them harder to get out. Don't know how true that is, but it's an approach that worked here. DD2 had a lot of gas, and severe reflux, which as has been said, often go hand in hand.