What Causes Blisters On Knee After A Knee Replacement?

I had a knee replacement a month ago First I developed large blisters around the cut and down below and around the knee those blisters die down now but I have a swelling still in the knee and down my leg to my ancle with crazy itch that drove me crazy I wouldn t hide that I scratch it from time to time I tried different lotions and steroid cream that my doctor gave me nothing helps My family doctor sent me for an ultrasound last week and there was no blood clots that show she gave me one pill to drain the water if there is any I am still the same any ideas