Burping help

I can not for the life of me get my son to burp after he finishes his bottles. Sometimes he belches but today he hasnt burped ; but he farts just fine. Does anyone have any tips of how to get my son to burp? I'm going nuts trying to pat his back for an hour at a time... and he falls asleep after 15 minutes of my trying to burp him.. any advice please😟😥