This is critical to get in to a vet. This inappropriate and frequent urination could be due to a bladder stones, urinary tract infection, or even bladder tumor. All of which could also result in abdominal pain!
But, with the abdominal pain, whether related to bladder or not, he really needs to get a full assessment by the vet. That should include a basic blood and urine test.
These symptoms cannot be moderated at home with over-the-counter therapy, and considering its been two weeks with the inappropriate urination, we know this problem will only get worse.
The vet may also suggest an abdominal x-ray if they can't identify why he is so painful.
Wish I could do more, but hope that information helps.
I understand your worried, but he hasn't had a basic exam yet or any tests. That will help you!