Ouch, my knees!

Miles walked: 3.4
Weight: 241.5

I felt really good today. I walked faster and felt better than I have in awhile. I felt like I could break into a jog, and at one point I did but it hurt my knees too much so I went back to walking. I thought after walking for 2 miles that my joints would be loose enough for jogging, but I was wrong. What do I need to do to start jogging? Maybe I'm just not ready yet, huh.