Why doesn't he EAT?

Or should I say, "Why doesn't he eat his normal meals"?

He used to be a good eater, finishing his food within lightning speed of 10-15 min during most meals, till a few days ago.

Since last Friday, he'd been sleeping with Ah Ma, as we are trying to sleep train him by disassociating sleep with breastfeeding. At around the same period, he started losing interest in his meals. I tried changing his food, even giving him rice instead of the usual porridge but he just wouldn't eat. Even with fruits like papaya, pears n apples, at most he'd just manage a little n simply refused to take anymore. However, he liked milk. Initially, it was just breast milk during the day n he'd only drink a little if offered formula. Now, he loved both. N "junk" - plain bread n baby biscuits.

Why? Why? Why?

Is it bcos of the changes to his sleep arrangement? Or due to teething (but he already grew 6 n hadn't been bugged by this problem before)??