I had a cementless hip replacement 3 yrs ago and have started having mild pain which my doc thinks is soft tissue injury, what can I do for it?

Rehab. First make sure you have consulted with the orthopaedic surgeon who performed your surgery. If xrays are normal, then physical therapy can often address any type of soft tissue pain.
Rest. If the pain does not improve with rest or physical therapy, x-rays and other tests may be necessary to make sure the hip is not loose or infected.