You have to listen to the doctor, they don't say 4 times a day just because, there's a reason that has to do with the bioavailability of the drug and the probability of toxic effects.
Pain *****, but having stomach ulcers or many other things, is much worst!!! You can ask him to change the painkiller, but don't take more times than recommended!
You need to approach your MD from a different perspective. What you need is something for breakthrough pain. Ask for something long-acting and then try something fast-acting for those times of exacerbation. There are many things you can try. You don't say what you are on; but having to take something 4 times a day is not the way to go for chronic pain, that is for short-term acute pain that goes away after one or two doses. I take something every 12 hrs. and occasionally need to add a dose of Tylenol here and there. I have Lyme arthritis, peripheral neuropathies, painful lesions on my scalp and muscle spasms. I am now having more better days than before with this med regimen. Talk to your doctor right away. Good luck!