In reply to Paul Troon:
You describe it just as I have been suffering for a few years. I was recommended some piriformis stretches, and within days it was much, much better.
I have tight hamstrings too, from cycling and a lot of hill walking, and when I ignored it, it manifested itself as you describe, and them a real nasty bout of what I thought was sciatica.
As I said, the 'pigeon' yoga stretch, or one where your partner assists you is almost immediate relief (google them, there's load). It never goes away totally, but at 50, I accept my body is less flexible now, and stretch far more than I used to.