Suggest Remedy For Severe Pain In Lower Back While Going To Sleep

Hello, I have been having problems with my back when I lay down to sleep at night, only when I go to bed, it hurts so bad at night I can't sleep, it is on the right side, lower back, if I lay on that side I can hardly get up at night, it ache so bad, if I get up in a chair and put the heating pad on it and I can walk around all day and do anything I want and I have no problem, only at night when I go to bed. Can you tell what is wrong, went to Dr. they said my urine was clear and they didn't fine anything wrong with that she gave me some cream to use for a yeast infection but that is doing me no good.