I had a sex on my first day of my menstruation Oct. 27 2013. Can I get pregnant even if I'm in my first day of menstruation that?

Yes, you can get pregnant on any day of the month, including the first day of your period. However, the chances are much higher between periods.

Yes, pregnancy is possible any time you have sex. Unless you're tracking ovulation by using basal temperature readings every day, and tracking for at least 6 months (a year is better) there's no way for you to know when you ovulate. Even with tracking you could have an off month and ovulate during your cycle.

If you're having sex, pregnancy is possible. Being on your period doesn't make it safe.