Hi, yes I experienced knee pain coming into the third week as well, it was quite painful. I visited the DR and it was on the lower portion of my knee and it was diagnosed as bursitis. I took a load off for a few weeks, iced it, and took aleve twice daily. Then after chatting with a few runner friends, it was concluded that i needed running shoes, I was wearing some Nike shocks, that were about 2.5 years old. Did some research and found some Asics that were about $80, now i'm into week five and I feel like I'm running on clouds. Literally. So, I'd visit a Dr. just to make sure nothing serious happened, but that was my experience.