Sore Behind Knees More Condition_symptoms Hello I Have A Very Sore And Annoying Leg, Behind My Knee?

Hello I have a very sore and annoying leg, behind my knee? - sore behind knees more condition_symptoms

Was good for months at a time, became very swollen and fluid retention such as or something. If I even for a minute or an hour, then I do not lift my right leg stretched and is now very painful and little by little I have to stoop to take. I went to the doctor and he thought it was a baker's cyst. He had an ultrasound, but show nothing. My concern is cancer or something. The doctor said there is nothing I can do to treat my leg, and basically I have to endure the pain, etc ... It is only natural that I should endure the pain .... Please help ... What do you mean?