left lateral knee pain

I'm training for my first Ironman, I was running a couple of weeks ago and slipped on some ice, I didn't fall but I was off balance. The next day I went out for a run and the outside of my left knee started to hurt. I took a few days off and the knee still hurt. I took a week off, tried running this past Tuesday and about 2 miles in it started to hurt again. I will take another week off and try again. It is feeling better and it only hurts when I run, I can bike without pain. Some people have told me it's my IT band, so I've been stretching a lot. I think it might be my meniscus. Should I not bike as well? Get an MRI? Any thoughts out there would be greatly appreciated!!