Both ladies had great advice for you.
For me, this is how this whole training thing works... some days I have pains in areas I didn't have before. In a day or two they go away. I do have some painful areas that always pop up, I won't have a serious injury running through those pains, so I just ignore them.
If you knee is tender to the touch, it certainly wouldn't hurt to ice your knee after each session to see if that helps some.
Yea, I remember last year when I was training for my Half Ironman... at one point when I ran my knees would feel like they were inflamed and they hurt like heck. It was an odd pain and stayed with me for about a week or two. Then all of a sudden it was gone. I never stopped running or anything, it just stopped.
In training, you have to find that delicate balance of knowing your body well enough to know when to push through or to stop. The longer you stick with all of this, the more intune you will become with you body.
Now, aren't you the one who asked about running form... and you commented how your form changes based on if you are running on a treadmill or outdoors? Your running form might affect how your knee feels and not having a constant form might affect it as well. But I'm just guessing on that one. Wahine can maybe weigh in more on that.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"