Causes of some minor pain and aching in hip joint and upper thigh discomfort after total hip joint replacement?

Depends: Thigh pain in the front is usually from scar tissue from the hip joint tightening up from sitting too much. Stretching the hip and quad can help. Pain in the upper thigh behind the hip is usually from sciatic nerve irritation in the lumbar spine, or infrequently from scarring at the surgery site. I would ask your orthopaedic surgeon.

Various causes: A common cause of hip pain after hip replacement is greater trochanteric bursitis. Another cause is gluteus tendinitis. If the pain is severe you should get an x-ray and infection is also to be considered.