knee/cleat placement

just wondering, today on my ride (40 miles) my left knee was feeling annoyed after say the first 30 miles, sort of toward the outside of the knee. It is still feeling this way several hours later. I would describe it as feeling like it wants to lock up and not be bending.

I had a cleat fall out on me during a long two day ride (beginning of August) and the techs put another one on my shoe for me. We eyeballed it and I think the placement's good, but could this be the cause of my knee pain? I've never had the issue previously, and I haven't gone on any rides in about 2.5 weeks so the legs were plenty fresh. My other rides post the big ride were either flat, short, or both.

Aside from that, I felt very good riding. How can I figure out where the cleat should be, if it is likely it's the cause of my pain? Otherwise, is it just because I haven't ridden in a while? Can the muscle alter that quickly?

Thanks.