I had unprotected sex with my girl friend on december 3, 2015. on december 10, 2015 she had her menstration.. is there chances of pregnancy?

Pregnancy unlikely: A girl cannot get her regular period and be pregnant at the same time. However, she can get pregnant a week or two after her regular period. If she has some spotting or light bleeding that doesn't look like her normal regular period, she can check a urine pregnancy test about 3 weeks after sex (3 weeks after when conception might have happened) to see if she is pregnant.