My left breast has been itching for a week. 2 weeks ago I had a mammogram and ultrasound where they found sists filled with water. Could this be the problem

No, but ... Cysts are benign, and unless symptomatic require no treatment. Red or itchy breasts should be evaluated if persistent. Infection or, less likely but more worrisome, inflammatory cancer can present without findings on a mammogram.
Would . Would anticipate that your doctor would have told you if the cysts evaluated via mammogram and ultrasound were worrisome. The itching is likely not to be associated with the cysts.