Help mamas! Breastfed baby refusing to eat.

My son is 9 months old and breastfed. This morning he has REFUSED to nurse. He was crying and crying, but would not even attempt to latch. I got him to eat a jar of baby food and take a few sips of water and now he's playing happily, but he's never done this before. He's never taken a bottle, but I pumped and stored what I had from this morning anyway.

What should I do? He doesn't have a fever or anything and seems perfectly content now. Is this a nursing strike? I feel like he's too young to be trying to wean, especially since he's never taken bottles. He has a checkup tomorrow so I'm going to talk to his doctor about it, but I'll call them and try to get in sooner if I need to.