I don't want to worry you, but I wouldn't wait until Monday. I forget, was he in a shelter environment? Around a lot of new dogs? The symptoms sound like parvo. Does the diarrhea have a horrible stench? Worse than 'regular' diarrhea?

Vomitting, loss of appetite, and bloody diarrhea are tell-tale signs of parvo. *Hopefully* and fingers crossed it's just a little bit of an upset tummy, but I would get him to the vet....