May I ask a few questions?
Is he urinating normally?
When was the last time he urinated and had a bowel movement?
Is he eating normally?
How many times did he vomit?
How old is he?
Has he always been a picky eater and big water drinker or are these two things that you've recently noticed?
I think these symptoms due warrant a vet visit. In the meanwhile, you can safely give him 1/4 of a 10mg pepcid every 12 hours to help control nausea.
In a cat that age, those symptoms could indicate constipation, urinary infections or obstructions, kidney or liver disease, and diabetes.
All of those can be ruled in or out with a physical exam and some routine bloodwork.
Good luck and let me know if you have any further questions.
You can try mixing a little canned pumpkin in the food. And keep plenty of water available. Sometimes that helps move things along.