Picky eating??

My 1 year old used to eat all his meals super super well and was quite a good tooth for it. He’d love to eat so much and ate whatever I gave or had for myself for that matter. It’s been about 2 weeks now where he no longer finishes the same quantities he used to eat and will very often reject the food I give him. He now wants to breastfeed a lot more. But I’ve always been an under supplier and he’s stopped nursing for meals a long time ago so I’m also producing less than I used to so he obviously can’t replace his meals for that anymore to the extent that he’s doing it. I have no idea why this is happening or what to do honestly. He went from eating a whole chicken breast to less than half a pancake. He likes his cookies, bars, gerber puffs, cheerios and vegetable puffs but not the real meals 🙁 What is this and how do I get him eating the same way again?