I have been doing a lot of research on Lupus as my oldest daughter was recently diagnosed. Lupus can affect cartilage and other connective tissues. You might want to ask your doctor to do an ANA test on your blood. I sincerely hope you don't have it...
I have seen the doctor examining and looking for a hernia and he has asked the patient to cough because this pushes out the stomach muscles and the hernia can be felt then.
I just read an article today that said doctor's cannot easily diagnose a hernia if the patient is lying down. When I went to the surgeon about a hernia, he had me stand and push my tummy muscles out. He was able to find it right away, then.
Don't know whether this could be a hernia.
I would suggest you make an appointment to see your doctor or a different on in the practice and tell him your concerns. If the doctor does not suggest it, ask if you can have be sent for further investigation, like an ultrasound scan.
Best wishes.