My baby wont burp?

hi i have tried all the usual positions when burping my baby also i have tried colic drops,gaviscon infant and infacol which all have no effect.Also everytime he poos its diarea and he will fall asleep on the formula feed after 2ozs while before hand he would drink 5ozs no problem.i cant seem to get any burps out of him can anyone help plzzzzzz. thanks for any help at all.