What Causes Pain In The Legs Post Kidney Transplant?

a few eeks back, I got a dull achy pain that ran down both legs making them weak and extended from the butt too. It lasted two days, I had seen the doctor and he said maybe back pain/pinched nerve and sent me home. I can not take nsaids as i have had a kidney transplant and kidney specialist said not to worry as it was first time but it has started this morning to point i cant climb up stairs