Thanks for the advice everyone. I haven't called the vet yet. I was thinking about it and every time it happened it's been at a time where my parents had been watching him (while I was at work)...and they don't always watch him that well...they forget to close the basement door and he goes down and eats Reggie/Sydney's food. I don't know if that is it or not. He's very sensitive, when he was a pup I fed him pedigree and he had diarhea constantly...if he gets any lower quality food that seems to bother him.

I didn't think about worms. He's on heartguard which it says on the box treats and controls ascarid and hookworm infections as well as preventing heartworm. I guess he could have a different kind of worm though?

He acts completely fine at the moment. The last time I took him to the vet for this (diarrhea and vomiting) was quite a long time ago...they did a stool sample, x-rays and a bunch of other tests. They found absolutely nothing wrong and it cost me a ton of money ugh...I just don't want to have that happen again.