Is my gf pregnant if we had sex 8 days before her regular period then 8 days later she had her regular period, or ill have to wait another month if she has irregular period? does the scenario makes her pregnant?

Depends on details: If a woman has a regular normal period after sex, then she is not pregnant. If she cannot be certain that her bleeding was a normal period, then she could possibly be pregnant. A urine pregnancy test (available in stores everywhere) done 3 weeks after the last time she had sex will give the answer. Be sure to read the instructions and do the test correctly.

Pregnant ? : What is described does not automatically represent pregnancy, however, pregnancy is possible, so get a home pregnancy test or if possible a serum HCG (pregnancy hormone) test from a lab or your physician's office to be certain.