Your doctor is likely to do a DRE (digital rectal exam) don't worry this is no fancy computer probe, digit means finger. They will ask you to lay on you left side and pull your knees up to your stomach put on gloves and a lubricant and gently insert one finger into your rectum, I have had a DRE for piles and never felt a thing, diagnosis, old fissure and some piles but receding piles do no treatment apart from a stool softener needed. They will check your prostate, as it can be easily felt via the rectum. Going to your doctor is nothing to worry about.
My stepdad is in his 80s and has prostate cancer, the treatments are AMAZING. Chances are you have some other benign condition causing this such as IBS and a problem with your hip muscles. They may send you on to a physio for further testing of the hip.
DO NOT WORRY. Best to get it checked out!