Knee pain going down stairs and while running

Hi All,
I have been having a 'piercing' right knee pain 9/10, after running (forefoot strike) some hills.
The pain got worst during down hills and calmed down during flat or up hills, I kept running with the pain for another 3km.
After my run I went to sleep for 2 hours, when got up had pain lifting my right knee up while walking, the pain seemed to come from the lateral posterior region.
Taking the stairs down from my flat was as painful.

Today, after one week of rest and no runs, the pain only exacerbates taking down the stairs, when my right knee is on the stair and the left taking the next down, the pain is piercing as the left foot is almost touching the stair, while my right is bent at the knee and ankle. The pain seems more inferior-anterior-lateral, somewhere around the head of the fibula.

I got full ROM at both knees, less dorsiflexion ROM at my right foot and I feel as my right knee goes medially during midstance.

I will appreciate your help.
Cheers,
Tom

Why don't you try knee stretches like Chair knee extension, heel slide knee extension and knee flexion.