My girlfriend's period usually 31-34 days now she is on 45 days. she had bleeding i don't know if it's implantation bleeding or period. it's was 17 days since we had protected sex. how do i know if it's a period or implantion and chance of pregnancy?

Do a home pregnancy test. If the result is negative repeat the test 4-5 days later unless she gets a period by then. Use first morning urine and follow the instructions carefully. Wish you good health! If you do not wish to be pregnant, use contraception all the time, every time. Consider implanted contraceptive, or IUD. Practice safe sex. Get HPV vaccine,