Why won't my dog eat?

Okay my dog Paddy (he's a boy) he won't eat his dog food every other time give it to him, but today i found him nibbling at the soft and wet food. But when I poured our the wet food and put in crunchy fresh food he walked away. He is about 10 or nine months and 47lbs. My mom thinks he's teething but i don't know. He is going to the vet Friday. Thanks for your help! :)