Riding him

Okay I have a problem and I don’t know what it is or what to do about it. When I’m riding my boyfriend, after 10-15 minutes I get a very sharp pain in my back just above where my kidneys are. I’ve tried adjusting my position by leaning back/forward, repositioning my legs, adjusting my center of gravity, you name it. The pain usually dissipates in a few minutes if I get off him but it will start back up if we continue. This is the ONLY position where a feel pain and I’m talking some serious damn pain. It makes me feel bad because he LOVES when I’m on top but I can’t handle it anymore. Anyone else? I’m going to talk to my doctor about it soon but I was wondering if anyone else gets pain in their back too or if it’s just me?