Dealing with Knee's

On Saturday I ran 5 miles on the lakefront here in Chicago. It was so nice I had to take my shirt off I was so warm. Now, the problem is my left knee is still hurting a bit from the Shamrock Shuffle. I was able to finish the 5 miles but not as fast as I would have liked. I have decided to not run a 5k this weekend so I can let my knee heal. There is a different 5k at the end of the month that I think I'm going to run instead. Today I'm going to sign up for the Chicago Marathon. I am not sure why, but I have been waiting to see if I really wanted to run it. I am kinda scared I won't finish, but I plan to join a running group that meets on a regularly so I can train.