I'm on the pill negative tests could i be preggers?

had in march, on the pill for two years, first period i had was two days late. took two tests which both came up negative. now this months period only lasted an hour, took four tests, all came up negative... my sister had a cyst on her ovaries which made her not have a period... is this hereditary or could i be pregnant? i used three different types of pregnancy tests help?