possible ITBD pain but wanting to know more or ask for help to see why i have knee pain

I am not a frequent runner but am running the nyc marathon. I have run longer distances a few times and more recently during and after running had side knee pain on my left knee on the outside. I talked to some friends who said it could be IT band related so I ra today making sure to stretch a lot before running and after and I am still feeling a lot of discomofort. I will note when I was tretching my hips in the front are VERY tight. doing a lunge can sometimes be uncomfortable bc of the tightness and doing a lunge + leaning to the side really stretches.

any and all advice or information is helpful and appreciated.