Thanks for posting your query.
According to description, swelling seems to be due to synovitis
Due to inflammation of synovium or bursa fluid collects and causes swelling.
I encourage you to consult an orthopedician for physical examination. A few blood tests, X-rays of the knee, aspiration of swelling and send for microscopic examination will help us diagnose the condition and help us in choosing the best approach of treatment.
In the interim, you can take anti-inflammatory drug like motrin
to reduce pain and inflammation and rest well.
Wishing you good health
Dr Saurabh Gupta