perscription diet pills

We got him back on a Saturday and by the evening he ate a small meal and went to bed early. Sunday he woke up back to his old self again, ate his pill and his breakfast and played all morning, ate a healthy dinner and went to bed at normal time. Monday his stool got runny again and by Thursday Night, he began vomiting an hour after every meal. Its now Saturday morning and he hasn't held a meal down in 12 hours with the exception of a little white rice we steamed for him around 5pm. Now he has no interest in food and he has vomited 3 more times and it is a white, foamy slime comming out. He wont drink water either now. All he does is lay on the floor and then get up to go vomit. He hasn't held down one of his perscription anti-viral pills for 3 days now. We've tried feeding him is Perscription Science Diet IQ, and his regular Innova Puppy food and he has no interest in either. He wont even go after a potato chip that falls on the floor.