It could be your sacroiliac joints. They can do injections there. My doc says whenever people mention their butt hurts, it usually is the sacroiliac joint. Mine starts at lower back on each side of the spine and the pain travels across the buttocks down my leg and feet. Try Voltaren gel. It has helped me quite a bit. If I apply it as soon as it starts it prevents it from travelling any further.It is a prescription topical NSAID.