Mine is in a similar spot. It almost feels like a pinched nerve and it'll come out of no where. It lasted 4 days before I looked into stretches for it, it was affecting every day walking AND laying down for bed. Not okay! But, yeah absolutely I'll share what I do! I'll try directions and see if I find photos. They are basic and you may already be doing them though... The first two I always do is the butterfly stretch, I push down on my knees and lean as far forward as I can. Then from the butterfly like.. when you have one leg still tucked in and the other stretched out? You lean into your foot pointed outwards and then also turn away by using the bent leg and place your hands on your knee and turn. Make sure to hold those for the same amount of time. The last one is placing yourself in an almost push up position (face facing floor) fully extending the leg on the side of the pain (like for me it's the right hip so right leg) and tucking the opposite leg up and into your chest and lean forward and push your hips down but not touching the floor. I also switch legs because when I tuck in my right leg it feels good on my hip.
This is the second stretch because my directs are probably batty haha
http://img.ehowcdn.com/article-new/ehow/images/a02/68/3r/stretch-hip-flexors-800x800.jpg
The last stretch kind of looks like this, I just tuck the leg up further into my chest
http://www.drbackman.com/yoga-hip-sma.jpg
This was recommended to me, but it didn't help me too much. I figure it doesn't hurt to try it though, maybe it'll help you!
http://www.easyvigour.net.nz/fitness/pilatessketches/HipFlexStrFin.gif
I've found stretching after a run is way more effective too. I hope at least one of these you haven't tried and helps you as well. I wish you luck!