I horse back ride. suddenly in the past month i've noticed a pulling and achy feeling in my lower back while riding. kinda where kidneys are. ideas?

Back pain: You have back pain of some sort. Possibly a lumbar sprain with the strain of "up and down" horse-back riding. Your kidneys are more in the middle of your back as opposed to lower. Difficult to DX over the computer, see your dr. For an eval and if you notice a correlation to h-b riding and pain, hold off on the riding until you get the area looked at. Good luck.