In which knee pain becomes too much

I managed to get through Zumba class tonight... but just barely. THe pain in my knees is becoming worse. Until this week the pain was centered on my right knee. Now both of my knees have been hurting. The pain exists even when I am not exercising and hurts a lot more when I am sitting down and my knees stay in a bent position. All the pain is in the back of my knees. I can't stop exercising. I need it to get healthy again, and also because the only way to help my liver is to exercising. I do think I'm going to have to make an appointment to see a doctor about this. Soon.