Birth control pills are a constant. If you don't take one and you have had sex, there is a possibility that you can get pregnant. Now, if you took one after and you had sex during those three days, there is also a possibility that you can get pregnant. Birth control pills are not like the morning after pill. Question, how old are you?
The chances that you are still protected from being pregnant are minimal. This is because it is recommended that you take the pills regularly for increased chances of not becoming pregnant. You should follow the cycle you have been given. Consult a doctor for more help.
Birth control pills should be an everyday thing. I will also help calm your period. But, back to the topic, even if you are on constant birth control you can still get pregnant. Just like if you use protection such as condoms. The only 100% way to stay pregnant free is to not have sex. Anyways, even with the 3 days of birth control you have the chance of getting pregnant.