What Is The Swollen Right Knee?

I have a puffy swelling behind my right knee. There are also a series of 3 lumps on the outside back of my knee going north in direction. The first lump I noticed shaving about 3 months ago. Now there are three lumps and although they are not huge, they are very tender. The first lump was pea sized - now it's more almond sized.My calf and lower thigh often feel cramps. Went to the doctor who gave me a blood test and said it was normal. I am in mild pain all the time. What could cause this and where do I go next for treatment? I am 41, 135lbs, 5'3".