Prednisone can be a miracle drug, but sometimes, the side effects means that it doesn't work in real life. The fact that if you miss only one pill, you are in significant pain is another indication that this may not be the drug combination for you. And when you have arthritis, weight gain isn't a good idea, as it can become a problem for you joints.
In terms of painkillers, there are many different types out there - anything from Tylenol, NSAIDs (nonsteroidal anti-inflammatory drugs), Cox-2 inhibitors like Celebrex and Mobicox and opiates like Vicodin.
However, I wonder whether your current dose of methotrexate is too low or if it's still the right disease modifying drug for you. If your current dose is not controlling your RA well enough to give you significant pain relief, maybe you need to talk to your doctor about increasing the dosage. Or maybe the methotrexate needs some help, in which case you can potentially add another medication instead of prednisone (Plaquenil, Arava or one of the Biologics). Or maybe you need to switch to a different drug altogether. It's quite common to develop a tolerance to whatever medication you're on or for it to stop working as well as it used to, but the good thing is that in terms of medications that suppress the immune system and therefore your RA, methotrexate is near the bottom of the ladder (so to speak), so there are a number of other options for you.
Don't be shy about telling your doctor exactly how you feel and how much of the pain is interfering with your ability to live your life. Maybe it's time for discussion about what your other options are.