Hi slick, I've just started playing heel up and won't go back now! I find that (w/ my limited playing) I get some pain in my upper leg/hip and have to take a break after about 20-30 mins of playing and do something else for a while. Could you have pulled a muscle? That unfortunately does take a while to heal--you might consider seeing a dr since it's been going on so long. You could try stretching out that quad muscle by: standing on the left leg--bend and pull your right leg back behind you and grab w/ your right hand so that your knee is bent all the way and your heel is at your butt. Pull your leg back at the hip to stretch that area out. You see runners doing this alot.
 Not sure why you injured this--I haven't been playing long enough. I wonder if you're keeping that area tensed up too much all the time while you're playing? Try working on consciously relaxing that muscle group while you play, so that you're not using so much effort to lift your rt. leg. Sometimes to give myself a bit of a break if my upper leg is getting sore, I will brace a bit against the snare betw. my knees and that seems to rest that muscle group a bit. Or you can alternate w/ some heel-down to rest the muscles. Make sure you are using good posture, not slumping over, not leaning towards that right side. I find myself wanting to lean a bit to the right when I play heel up, and have moved my throne over towards the kick pedal a bit to compensate. A more supportive throne may help you too.
 Do you exercise regularly? Try walking at a good pace, large swinging steps. If that makes the pain worse, stop doing it for now. You just may have to rest for a few weeks and give this muscle a chance to heal up. Then stretch and exercise to make sure it doesn't happen again. You can do some real easy situps on a regular basis to strengthen your abs, since that seems to be affected too. *Note to those w/ back problems!!* Strengthening the abs will strengthen your back! Easy leg lifts will help strengthen that heel-up kick drum muscle group too.

Good luck, don't sweat it too much.
robyn

+1

also, sounds like you have bad technique.  might be a good idea to have a proper teacher teach you proper technique.