periods came a day late, now i'm feeling nausea?

Hi,
Welcome to ehealthforum,
When you are on hormonal birth control, you do tend to have shorter and lighter periods due to hormonal changes. Other possibility could be pregnancy (women can get pregnant while being on the birth control). Wait and watch for your next periods. Look out for development of any other new symptoms if you suspect to be pregnant. If you do not get your periods or if you get altered periods, or if you develop any symptoms suggestive of early pregnancy, consider visiting your doctor/gynecologist for examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately).
Take care.