How To Prevent Pregnancy?

Hi, I am 3 years old lady, married. My menstruation is not regular, it happens 2 or 3 months later each. My last date of menst is th december 2009. Today, at the time of intercourse, for the leakage of condom probably sperms has entered into. Then is there any probablity of being pregnant of mine. Actually I dont want to take baby at this time. How can i stop my pregnancy. If i take ECP, will that help me? Will the ECP will cause problem in later. plz help me quickly. I am in tension.