Hi Matt, welcome to Yorkie Talk
Ok, I'm not a vet by any means, but here's what i'd suggest to start with:
The first and easiest, cheapest thing to do is take a stool sample into your vet and have them check for parasites.
Next thing, bloodwork - a full comp./CBC (those two things along with an exam should cost somewhere around $100)
It does kind of sound like a kidney problem, but he's so young. Is there any way possible he could have gotten into something toxic? How long has this been going on? The other thing that would cause excess drinking and possibly a few of his other sympoms is diabetes, but again, he's really young.
Idk what to tell you other than he absolutely 100% needs to see a vet asap. Talk to your vet before hand about budget, have them start with the most conservative things (like the stool check and bloodwork). Was he vaccinated as a puppy? There's just a bunch of things that need to be figured out by a vet, there's no way around it. If you need help with the vet bill, look into CareCredit (the vet you see must accept credit cards to use this though). Good luck, do what you have to to get him to a vet for at least the basic testing (if it is kidneys, they'll know by simple bloodwork).