I believe this is the same that I had been suffering from for a few months this winter after changing out my shoes (story of my running life). While I never had it diagnosed, after reading about the symptoms...which for me were the knot in the butt as well as a deeper pain in what felt like the hip joint...I thought I might have acquired a shorter leg on one side which I understand is very common. I thought about getting evaluated to see if I needed a lift, but time got away from me and I never made an appointment.
I kept running, although I cut my mileage way back, wore my ice cleats religiously and stretched the butt/hip muscles for a loooooooooooong time after warming up. Because it was hard to target the area as far as icing goes, I would take 3 ibuprofen after each run and that seemed to minimize inflammation and soreness. It finally is to the point where I don't notice any stiffness or tightness in the area. I hope it goes away for you as well.
