Unable to make left knee straight. Walk.

Unable to make left knee straight due to pain after viral fever. I got viral fever 6 weeks back. All reports dengue typhoid chicken guniya are normal but I had sever body pains. I used medication, during medication I got no pains, after 2 days of stoping tablets severe pains. Later I started using naproxen 500. I dont use it daily, whenever I get severe pain, sometimes continuosly 3 days. All joint pains reduce but my left knee joint pain is severe and cannot make it straight n walk normally even though I take naproxen 500 tablet. This left knee pain started the night before I got viral fever. I thought it was due to lunges I did in gym but it is not going from 6 weeks. I am worried. I am scared to wake up as am getting severe pain in left knee joint when I wake up to walk. With great difficulty I walk to bathroom by bending it. All other joint are also stiff but it is bearable. My left knee joint pain is something am unable to bear while walking, I have to bend a little and walk.