I am currently having pain behind my right knee and at the same time my right foot
Feels numb and some pain - what may cause this?

Two possibilities are pressure on a nerve or some kind of circulatory problem. Both are important and can get worse. The solution might be as simple as doing some exercises. If it's nerve related, the numbness and pain in our foot is a kind of neuropathy or paresthesia. You might look at wrongdiagnosis.com to get some more ideas. If something basic is causing the problem, like you are getting type 2 diabetes, you need to know about it. It could be important or no big deal. I would see a doctor and not allow them to dismiss you until you feel satisfied that you know why it's happening and have a treatment. Good luck!

PS. I have the same, but I also have severe back problems and a spinal fusion and the doctors have told me to try to control the neuropathy. But other things can cause tingling in your foot.