Yes there's always a chance of pregnancy if you're having unprotected sex, however if you had sex a day before your period
, it's very unlikely, if you mean by contraceptive pill you mean plan B
, it can cause very irregular cycles and symptoms, so wait 2 weeks from the unprotected sex and take a HPT it should be positive by then. If you're not trying to get pregnant you need to use some form of BC, Plan B is very bad for your cycles/reproductive system and shouldn't be used as BC. Good luck!