What Causes Pain In Lower Right Back And Upper Buttocks?

i feel deep pain in my lower right back and in the upper buttocks. i was wondereing could i have pulled my iliacus muscle. the pain is constant and dull. it gets a little sharp when i sit. But when i got to bed it doesnt hurt. i benn two days sinc i have felt the pain. Also if this is a pulled iliacus how long should i feel pain and how long do i have to stay of any activities like basket all and running