Knee Pain

I'm using the Run 5k app to train me off the couch. I'm in week three and my knee suddenly started to hurt when I put my weight on it to walk and run. It started when I was walking oddly enough. I run every other day and do cardio on the off days. It's my second run since this started and it's worse. No swelling and it doesn't look off but if I try to walk normal the motions from bent to straight hurts. Should I be worried?
I looked like one leg was longer than the other when I ran today.