I agree with Fishman - nearly everyone has some ailment that they have to learn to live with. I've had neck pain for years and I still don't know what causes it. I've been in a lot of pain for the past week with shoulder and arm pain, and I haven't a clue what's causing that either. Everyone has something!
You had a clear x-ray 2 years ago, and even though you still have the pain, it hasn't got any worse. Do you honestly think if it was something serious that it would stay the same for 2 years?
This is your HA mind trying to push you down the rabbit hole. You need to push back and acknowledge that the thoughts you're having are just thoughts and nothing more. Yes they're strong thoughts and they make you feel like crap but you have to keep repeating to yourself that they're only thoughts.
You know deep down that there's nothing serious going on.
I know it sucks because I've been there a million times myself. But don't let those HA thoughts win here, keep fighting them, show them who's boss