Sounds like you may have found your problem. I would stop doing any movements which aggravate the tendon immediately.
I just read a post where someone said they managed hip flexor problems by box squatting as this forces one to use the posterior chain.
http://startingstrength.com/resource...t=24964&page=1
I'm no expert on this but I had a lot of pain in this area at one stage. I managed to fix it by laying off for a couple of weeks and then coming back really light to 'test' if the pain had subsided. As I mentioned before though, my problems were a form issue.