Thanks for posting your query.
According to your description , knee pain
seems to be inflammatory in nature. It can be due to muscular strain.
I advice you to give you rest to your foot, take anti-inflammatory drug like motrin
1 tablet with food as and when required (upto 4 tablets daily) to reduce pain and inflammation and consult your doctor for thorough examination of knee and rule out any infective cause.
Wishing you good health
Dr Saurabh Gupta