Low ab/pelvic pain after run/yoga?

I did a 9 mile long run last Saturday and felt pretty good. My shoes are going bad and causing IT pain in my knees (I think), so I decided I'd lay off the running until I got new shoes this week. I did a swim workout on Sunday and then did 1 hour of power yoga last night.

After my long runs I usually feel a bit of soreness in my abs. I figure they're getting worked a bit. Saturday was no different. Last night I was getting into the prayer twist pose. Looks like this: http://www.yogabasics.com/asana/postures/prayertwist.htmlAs I was getting into this pose with my left leg forward, I felt pain in my left low ab/pelvic area from about my hip bone and then diagonally down. It was painful enough that I had to stop. Later in my DVD there's a section of ab work doing bicycle crunches. When I'd pull my right leg in and lower my left, I had the same pain and had to stop. It also ended up waking me up last night whenever I'd turn over.

What's really strange is that it doesn't really hurt when I'm not doing any of these things. None of the other lunge/squat type poses hurt. So does anyone know what this could be? I'm just not sure if I need to rest it or if I can do my scheduled bike stuff. Any stretches for that area? Thanks!

I'm still having trouble figuring out when to push through things that hurt or are uncomfortable and when to stop/rest.