What is wrong with this baby that I am babysitting?

I am babysitting a 10 month old boy. He woke up at 7, ate breakfast at 7:30 (baby cereal and one thing of baby fruits, plus 5oz of formula), then at 9:15, he vomited. He is not acting any different, he seems fine, but he may be a little warm/feverish. Also, on Sunday, he didn't eat anything all day and did not poop all day. Then yesterday, pooped almost twice as normal. What is wrong with him? I'm worried..