Before starting to run or jog or walk for long periods of time, you should have your core muscles toned. If I were you, I would go to the exercise pages here on Spark People and try the following routine - it actually took very severe pain from my knee in one work-out. I was absolutely amazed and could not believe it. These are the exercises I did. I don't know if it was one or two or the combination of all of them, but it DID happen;
1 superman, then while on your belly do 1 set of lying leg curls, then the other superman, then the other set of lying leg curls, then 2 sets of the pendulums, then 2 sets of the bridges, then then 2 sets each of both the lying adductions & abductions, then ending with 2 sets of reverse ab crunches.
I pray it helps you like it did me.