You need to seek after hours vet care immediately. When a cat does not eat, they are subject to hepatic lipidosis. This is where the liver thinks it's starving and starts grabbing fat cells. It actually ends up killing the liver.
You need to get immediate vet care. The belly pain and urinary issues could indicate a urinary blockage.
No matter what, go ahead and give your vet a call and either take him in or get a referral to an after hours clinic.
Let me know if you still have questions.