I'd guess piriformis or S-I joint. I have piriformis syndrome - all that means is I have a tendancy to be a tight a$$
LOL Seriously all it means is my piriformis tends to be too tight and cause pain/sciatic nerve pain. Also If I over stretch that area, I tend to get an achey hip at the joint - SI joint pain. If you google both of those it may help you determine if either sounds like the pain/twinges you're having. Or that it's something totally different
My issues were both diagnosed by a Physiotherapist which is what I'd reccomend for you too.
Beth