My boy is sick. Advice?

So we've already been to the vet, had blood work done and all that.

Past week or so, he's been really lethargic, sleeping a lot and most concerning, not eating/drinking much. He's not constipated or in pain that I can tell, the vet prescribed pepsid AC and an anti-biotic as the blood work showed an elevated white cell count.

I've had him run normally outside a few times since this has started and last night managed to get him to eat his whole bowl of food. Today, nothing. Couldn't even get him to take his meds with high reward treats...

Just worried about him is all, he seems depressed and I just want my fur missile back at 100%. We have a follow up tomorrow with the vet, but have any of you guys dealt with something like this in the past? No vomit, constipation, lameness...just laziness and minimal excitement.

:(

In positive news, he ripped the longest, loudest burp of his life when we were waiting at the vet on the weekend. They thought it was me. My fiancée had to confirm that it was the dog because I was still laughing.