Hi. Thanks for your query. Noted the history of continuous low grade fever for 8-9 days, severe knee joint pain, taking Acetaminophen and colonoscopy in past. Blood work normal except high sedimentation rate and Lyme s is negative. These symptoms considered together indicate that you may have septic arthritis that is causing low grade fever. I would advise you the following: Get an opinion of an Orthopedic Surgeon for clinical evaluation, examination and further investigations like MRI of the affected knee, tapping for fluid and sending the fluid for microscopy, tuberculosis, culture and sensitivity. May need a course of an antibiotic and an anti-inflammatory medications till cured. Further management will depend upon the clinical diagnosis added by the investigations reports.