Two of my sisters died from too late a diagnosis of ovarian cancer. how often should my doctor check me for this and what kind of test should be used?

Unfortunately there are no simple screening tests for ovarian cancer. Periodic transvaginal ultrasound examination may be needed in a high risk patient. Visit this site for info: https://www.cdc.gov/cancer/ovarian/basic_info/screening.htm

Would suggest starting with genetic testing at the cancer center where your sisters underwent treatment. Based on actual results establishing with a Gyn doc specializing in oncology would be best. There is otherwise no consensus in the guidelines regarding screening for ovarian cancer in high risk patients. A reliable site is cancer.org by the American Cancer Society.