I have the same thing with my guy. I burp & burp him but sometimes he'll wake up screaming & sure enough a minute later he burps. The one thing that sounds funny but helped is in the BW book, Tracy says to run your hand up (only) the left side of the baby's back. Believe it or not, this has helped get more burps out of Samuel. And I make sure I stand to burp him so his feet are hanging down & he's straight up.