My 11 month won't eat like he use to help!

My son is a very good eater. He loves food. Before a couple of weeks ago he would eat just about everything you put on his plate. For some reason this week he will take 3 or 4 bites and thats it. After a few bites he will either spit it out or won't open his mouth. I wanted to know if any of the other mothers are going through this? Do you think it's because he's teething? Or Is it just a phase? Please help me out cause I'm loosing it. I really want my good water back.