Hi I Have A Lump Under My Knee Caused By

Hi I have a lump under my knee caused by walking at 6 .5k an hour on treadmill for 50 min every day I start off at 3k an hour building up 6.5 and down to 3 k to warm down. I have had this about a week now initially my knee was swollen as well but this has subsided now after treating with fenbid forte 10% gel for the last 3 days.The pain is such that I cannot bend my knee any more than about 30 degrees therefore cannont drive or sit at my office desk without severe pain. In addition to the gel I have been resting my knee what should I do now. Thanks I do not have an e mail address but can be txted on this number