Shooting pain down leg ??

There are probably lots of things it could be, but one common problem is your ITB, especially if the pain is on the outside of your leg. Here is a link to a brief explanation of ITB injuries.

http://runninginjuryfree.org/2008/09/it-band.html

There are a lot of stretches for the ITB. Google the two words itb injury to get links to them. Here are the stretches I do

http://runninginjuryfree.org/2008/09/pictures-of-stretch-exercises.html

I do all of them before I run, and I repeat the ones for my legs and ITB after I run.

As a physical therapist in the sports medicine arena, I have treated this problem in runners before, especially in women.  You mentioned that it arises from your groin and travels down your leg.  If what you describe is on the inside of your upper leg, it might be arising from your adductor muscles.  There are several factors that can contribute to this including some asymmetries around your pelvis (SI joint dysfunction or muscle imbalances between the hip flexors and hamstrings), or weakness of the gluteals.  There are alot of things a well-trained PT can do to help.  If it were me, I would look for a therapist who is certified in ASTYM treatment.  In my practice, I have seen that runners can development fibrotic/scar tissue within the adductor muscle and it can be quickly and very effectively treated with this method.  You can check the internet for a certified therapist near you.  Good luck!