Bee, this is obviously because you are so lazy on day 7!
Seriously, many things ruled out. Not bone, not nerve, not bursitis, joint itself, which would be affected in many more activities/positions. Position (posterior), and nature is suggestive of piriformis syndrome.
Piriformis syndrome is a common cause of posterior hip pain in runners. This is deep buttock pain that occurs with running and can be accompanied by pain radiating down the back of the leg. The muscle is tender to deep palpation and stretching (hip flexion adduction and internal rotation). Treatment consists of deep tissue massage of the area, stretching the piriformis muscle, and strengthening the hip abductors/external rotators. This is a problem that usually takes weeks or months to get better with physical therapy.
Oftimes, if there is a specific action that triggers the pain, simply stopping that action will eventually eliminate the problem.
Anti inflammatory medications (NSAIDs) for a few weeks (at full anti inflammatory dosages) usually help a lot, some people feel.
Needless to say, progression of the problem, lack of improvement over time, REQUIRES a formal evaluation.
Some might feel that your lack of symptoms in doing normal activities and walking would merit a period of conservative treatment(stopping what hurts, massage, perhaps heat, stretching, perhaps an NSAID) on your own, so long as you don't get worse, and you seemed to get better on that approach.
