swelling of the knee & ankle

six weeks ago, i had arthoscopic surgery on my left knee. the condition of the knee includes baker's cyst, torn cartiliage, and pseudo-gout. i started physical therapy six weeks after the operation. i also started bicycling at a modest pace. after one week of cycling and one day of physical therapy, the area below the knee to the ankle became swollen. a "venus-doppler" test proved no presence of a blood clot. the swelling has fluctuated up and down for the past week and there has been intermittent low grade fever. i am currently taking advil. my concern is that my recovery is at best at a standstill, if not in regression. what are my options? i am 54 years old. thank you.