She isn't likely to get pregnant from unprotected intercourse the day before her period. It isn't impossible, but very improbable. Sperm can survive in her reproductive tract for up to 5 days. So, if she ovulates in the next 5 days (unlikely, women usually ovulate later in their cycle) she COULD possibly get pregnant. If you are worried, you can get her the Plan B pill. A pregnancy test won't give an accurate result at this point. You have to wait a few weeks.
Please do yourself (and your partner) a favor and use a condom EVERY time. Condoms not only help prevent unplanned pregnancy, they help protect against sexually transmitted diseases. Your partner can have an STD and not even know it. STDs can cause long term pain, disability, infertility and even death. You owe it to yourself and your partner to protect you both. You are WORTH protecting.
If it's a true period, then no she's not pregnant. You can't have both at the same time. You DO however need to start investing in condoms and birth control. Plan B isn't meant or made to be taken habitually, and isn't made to take the place of proper birth control or more than 2x a year.