Baby suddenly rejecting one breast?

Shayla • 🧔👩 👼👧👼👦👱‍♂️🐕‍🦺🐕 Happily married Mama Bear

So since yesterday evening, my 6 month old suddenly started refusing to nurse on the left side. I can't seem to figure out why. There's plenty of milk in it, he just doesn't want it. I've never had this problem before, and I don't know how to get him to take the left side again. He just pulls away and cries every time I try to feed him on that side.