You wouldn't have built up a tolerance of Oxy in such a short time, so perhaps your pain is getting worse. I know that I was on it for close to a year before mine had to be upped, but I had also felt that my pain was worse. Also, a lot of people on oxycontin are given a breakthrough medication like tylox (hydrocodone) for breakthrough pain. I don't know what dosage you are on or how many you are allowed daily, so it's hard to say if you're on enough to take away your pain.
Jo just posted about her dosage and how her doctor decided on the amount she should be on and it was determined by how many breakthrough pain pills she had to take. You should be able to find it easily as I know it was in the last few weeks.