Recurring Problems from Jogging

Just recently, I have been experiencing problems with my left knee after jogging. I am a recreational jogger (3-5KMs average). Been jogging for years. After a run, my knee tightens up and alot of discomfort trying to straighten it out. Takes several days, but the stiffness and discomfort goes away. Each day it gets better and better...Silly me, I try to jog again..no problems during the run, but afterwards, the knee begins to stiffen up. Keeping it bent is okay but trying to straighten it out takes a lot of hobbling and use before I can walk with it somewhat normally. The same cycle persists. I am able to power walk no problem once the stiffness is gone, but when I think I am okay after several days of power walking, and try to jog again, the stiffness/discomfort is back.

Any ideas what this might be.