After total hip replacement in january, i have pain in both hips , buttocks and back. what is wrong?

Spinal: Assuming your hip surgery went well and your surgeon is pleased with the outcome, then back pain with associated bilateral hip and buttock pain is likely spinal in origin. Degeneration (i.e. Aging changes, also frequently called arthritis) is the most common cause of progressive back/buttocks pain, and can usually initially be treated conservatively. See a physician if your symptoms persist.

Pain: Pain may be not related to hip your replacement but may be related to your back. You should consult with your surgeon and attempt to evaluate the source of your discomfort.

Not the hip: This sounds like nerve compression in your spine. Find a good physiatrist to investigate.