If it's driving you nuts, imagine how HE feels? No one here can tell you what's wrong with him. It could be parasites, internal pain, neurological, etc.
Call your vet. Tell them it's an emergency. Ask if they will arrange payments. Borrow money from friends or family. Use a credit card. Call your humane society and ask if they can direct you to a low cost clinic. Take a loan. Sell something.....
This cat is your responsibility. He can depend only on you, and you cannot let him suffer. It's just not right.