If your oncologist is telling you your blood counts are normal, that’s a good sign, however, an oncologist is not a gynecologist. It’s common that your menstrual cycle would be influenced by different treatments including hormonal therapy or chemotherapy used with breast cancer.
Some cancer treatments either mimic the effects of menopause or push the body toward menopause, and such changes might lead to longer cycles. If an 11-day cycle is more than twice your cycle, make an appointment with your gynecologist. The physical exam by that doctor and any tests he or she recommends will help identify any problems and put your mind at ease.