I have seen numerous posts about saw knees and other gripes.
I too have had these issues, and despite years of running when Iwas younger, it is all about; for the most part weak knees and connecting muscles apparently.
As such there are numerous exercises on youtube that are there to help. But having watched the Beeb's Truest me I'm a Doctore last week, they have posted soem strengtheining exercises.
Here is the link for the video clip; Ihope it helps some