As said earlier, it's your ITB. Loosen it off a couple of times a week and don't ride if it's flaring up too much. Get a massage before your race if possible.

Immediately after your race, go and see a reputable bike fitter - preferably a physio if possible - and get your cleat position looked at ASAP. Chances are you've got your cleat at an unsuitable angle, placing stress through the pedal stroke.

Do you used fixed cleats? Not a good idea at all except under very specific circumstances. I know that running brings on the pain and causes you to lock up, but the loading that is causing this will be occuring on the bike.