I figured it out!

I figured it out... my arthritis/illness is powered by the moon. I am part werewolf and I have inflammation or swelling because my bones are getting bigger due to the transformation but since I am just part werewolf  there is no full transformation. So every month before the full moon I will experience pain. That is my diagnosis and I'm sticking to my story. hehehe =)

It's a full moon out there so watch out =)