What Can Cause Delay In Periods?

i had sex with my boyfriend on 28th november for the first time.i don't know we had full sex or not.but when i got washed there were somefluid outcomes..my periods generally come on 29 or 30 of the month.but this time i did'n get periods till now.iam very worried.am i pregnant.? ifiam then how can i abort at home.please help