Hi there, and welcome to BW!
Congrats on your little one. I wouldn't worry about doing a yield. With my first lo, I breastfed him successfully for over a year, and could never pump much at all. The pump is not as efficient as your baby at all, I think it is more of a "learned skill" than anything.
You say diaper count is still good, this is great. My children would become fussy at the breast for a number of reasons, if they had gas, needed to be burped, were having a bowel movement, or if they were simply done and I was trying to get them to nurse longer. They can suddenly get more efficient overnight as well.
How long does your lo go between feeds when this happens? Also, at growth spurt times, Kate gets a bit fussier at the breast as well. When you end the feeding at that stage, how does your lo react to that? Does he calm down or still fuss?
Hang in there and don't panic. Your lo is still so young and it could be any numbr of things causing this, not neccessarily anything to worry about. Just keep an eye on diaper output, what goes in must come out!