Sorry about your knee Edgar. Give it a rest. You just did a 7 mile run on Sunday, and then a 4 mile run today - it may be a bit sore from that.
How many miles do you have on your current running shoes? 300 miles is about the average limit - then it's time for new ones. You might think it would take a long time to get that many miles - but it comes quicker than you think. Do you have more than one pair so you can alternate them each time you run?
Not sure if you do - but try not to wear your actual running shoes for any other activities - keep them just for running.
Are you stretching after running - especially after 7 miles?
Just some things to look at to see if it might be time for new shoes, or a change in surface (switch to dirt or trails - stay off of concrete if at all possible), or making more time for slow, thorough stretching after your run.