Right knee pain AND running

About 9 days ago, I went running on the treadmill on the gym.  I did my usual 3.5 miles. Ever since then, however, my right knee has been uncomfortable.  There is a slight burning sensation. There is no swelling, nor is it keeping me up at night. Sometimes, the dull pain moves to the back of my knee. It is not excruciating pain, but I know that it's there.

I had knee arthroscopy surgery 11 years ago on this knee due to a soccer injury in high school.  I have never had any problems with it until just recently.  I'm concerned however, because I was able to complete a short triathlon 3 weeks ago and had no problems.  

I've been trying to find out what it could be by reading info online.  
Is it possible that all I need to do is buy new running sneakers?
I also read that some women experience knee problems when their estrogen levels are highest in their bodies--Could this be a factor?
Should I continue to stay off of it, or should I try running again?

Any advice would be greatly appreciated!  I've iced it and taken ibuprofen but it doesn't seem to help.
Thanks!

[star queen]

Your symptoms lead me to believe you may have pulled or torn a ligament.  See an orthopedist and get your knee xrayed for a proper diagnoses.