I think my dog is sick

I got my dog a few weeks ago. He was up to date on all his shots except he’s due for a booster for his distemper vaccine soon.

He’s normally extremely energetic and hyper which is why I try to tire him out during the day. I work at a doggie daycare, boarding & training facility so I brought him to work with me and he ran around all day with the other dogs (all of our dogs have to be up to date on their shots as well). He was tired when we got home but still relatively normal. However he didn’t eat his dinner and only had part of breakfast. The next morning, today, he was hyped up in the morning but didn’t eat much breakfast. I took him to the park with my daughter all day and then ever since we got home he has just laid there, he also would not drink any water all day, he only ate a little bit of tuna I put in his food. he is hiding underneath my bed and behind the couch which I know dogs do when they’re not feeling well.

His breath feels hot and nose is dry but since it’s hot out (I did give him shade and offered water all day ) and now he is in AC I feel like he should be feeling better.

I got him to drink water when I brought the bowl up to him.

Idk this is really long winded and most likely he’s just tired from the heat and being out and about the past few days. But he has so much energy and is still a puppy (about a year they told me) so he shouldn’t be SO exhausted and not eating or drinking.

I guess I’m just venting cause I know I should just watch him and take him to the vet if he doesn’t get better. I just love him so much already, like it’s almost up there with my daughter I mean obviously not the same but I love him a lot he’s my little sidekick and I’m scared I’ve done something wrong somehow to make him get sick. He was completely healthy when I took him to the vet after adopting him :(

I mean does this seem like it could be serious or he’s just not feeling too well?

(He did have kennel cough when he came from the shelter but that went away a week or two ago also he is not coughing or sneezing no discharge from eyes or nose. )

Update... $173 later. He does not have Parvo thank god. And he is on antibiotics. And he ate some wet food and kept it down