Asking about my 3 week old breastfed son?

ok so my little baby boy is 3 weeks old and i breast feed him he was doing good keep my milk down and burping good to but for the past weeks he hasn't been bring up every good burps and when he dose burp he brings up just about all the milk he just drank im at my wits end he so cranky dont know what eles to do going to the doc tommrow but i was wondering if there is anything i can do in the mean time