More Breastfeeding Issues...

Kat
So my son is 6 weeks, and sometimes when I feed him, he will pull off and cry and cry. It's worrying me that he's not getting anything from the breast. I do occasionally supplement with formula if we are out and I can't stop to nurse him. I know he's getting at least a little bit bc when he pulls away there's at least a little milk in his mouth. I always put him back to latch on when he does it. I've only noticed he does it on one side though. Anyone have any ideas what could be wrong? Anyone dealt with this before? Tyia.