When does concern become obssesive worry?

I'm not quite sure what is happening to me. The past couple of months I have started having a pain in my hip and it is beginning to concern me. I started losing some weight and exercising more and since then my hip hurts worse. I thought it might be an exercise injury but it actually doesn't hurt while I am exercising. It hurts when I am at rest. It hurts especially bad at night, sitting on the couch or lying in the bed. It is not my sciatic nerve but rather if you stood with your hands down at your side it would be just above where the heel of your hand hits your hip. Or where the top of the leg meets the hip.....or where the bottom of your underwear hugs your hip......etc. It hurts to the bone. I can press on it and it hurts bad or I can just sit there and it hurts......a dull, constant ache. Sometimes the pain is felt all the way down my leg to my knee. I find it difficult to get comfortable. Aspirin, Ibuprofen, etc......does nothing to help. I am unsure of what to do.
I have panicked before and made my doctor do scans that showed nothing. I do not want to panic again. But I find myself reading the forums and searching the web for bone metastases. In the last two weeks I have spent waaayyyy to much time doing this. Its becoming obsessive and I'm not sure why. I've always said, and still feel, that if the cancer comes back then I will deal with it. There really is nothing I can do to prevent it from coming back. It either will or it won't. Do you sense a "but" coming? I think its the not knowing that is making me obsess. If I know what is happening then I can begin dealing with it. At least that's my story and I'm sticking to it.