I feel like I have the flu, but my right knee is very swollen and sore. Is that part of the flu virus or something separate? I'm concerned it's Lyme disease.

I am sorry to hear that you have been feeling unwell.

Flu can give you aching muscles and joints. However, it is unusual to give rise to a swollen knee and I would be looking at other explanations for this symptom.

Unfortunately, I am not able to work out whether or not you have Lyme’s disease from the information you have provided, but there are tests that can help us work this out.

I hope that this is helpful to you.