Friedabacal,
Sounds awfully familar...what you are describing could be 2 seperate things as well...the lower back/Coccyx pain is possibly your pouch pushing against the lower back as you said...(I get it on the front from my K pouch when full due to it being so low and pushing on my bladder/female orgains and hip area) and the other pain sounds like sciatic nerve pain...then again there is always sacroilitis which is an inflamation of the region (the joints in the pelvic/hip/sacrum region)...I feel like I want to yank my hip out of my body daily...if it is just inflamation (!) then it should improve with physical activity and anti-inflamatory meds (I use Advil type meds but a lot of pouchers do not tollerate them for very long)and do 1 hr or physical activity every morning...That gives me a few hrs of pure relief...if it is a full pouch pressing then the only solution that I know of would be emptying more often to prevent it from overfilling...for the sciatic nerve type pain you could try using the Swiss ball to stretch the zone regularly or some other exercises...sciatic responds to meds and stretching and sometimes bedrest but for me that usually makes it worse.
Sharon