I Have A Lump On The Side Of My Knee.

I have a lump on the side of my knee. I noticed it a couple of months ago and when I had my vasctomy I took Advil to easy the pain from that. When I was taking the Advil I noticed the lump on my knee almost when away completely but it seems to have come back. I've lost about 30 lbs in the last 4 months, but I wasn't that over weight. Was at 211 lbs Anyway I wonder if the lump was always there but started to notice it when I lost the weight. I do work out, but I do a lot of Cardio and not a lot of lifting. Any ideas if this is just some sort of inflamation?