My wife just had these exact pains, and it turned out to be her gull bladder. Basically, she was passing gull stones. Extreme pain in the lower back, on the right...vomitting, felt she had to shit but wouldnt...whole nine yards. Long story short, if she rolled around on the floor, sat in weird positions and shit...it would pass. In the end, they had to have that shit removed before it exploded and turned deadly. We were really hours before it turned fatal. The only way to see if it was about to explode...do an ultrasound. Id go to a free health clinic if it lasts longer than about 4 hours.