Iv been experiencing pain behind my knee. it hurts to walk on it. lasts a few days and goes away. this morning my foot was tingly, could it be serious?

See your doctor: Pain that severe needs to be worked up by your doctor in person. He/she will listen to you, perform an examination and possibly order some tests to see what's wrong with you.

Nerve issue: Tingly feet tells you it is a nerve issue but cannot rule out peripheral vascular disease as a cause. I would have a vascular and neurological exam to assess the cause. Most likely nerve compression at either the knee or spin level.