What Causes Stiffness And Pain In Buttocks?

i am 47 years old .my periods are irregular i.e.30 days, 45 days,etc.i have joints pain as well as severe buttocks pain to the extent sometimes i am unable to stand or bend.sometimes i am unable to do yoga alsobecause of stiff back and back pain. i don;t know whether it is muscle pain or nerve pain.i feel like i dont have strength in my buttocks and feel very weak.