What Are The Chances Of Pregnancy Through Withdrawal Method?

Could my girlfriend be pregnant while practicing pull-out method?
To make you understand entire scenario I will provide every possible detail. We are both 22 years old, study in a reputed institution in India.
My girlfriend's last period started on Jan 10th, (and second last started on Dec 20th). On the last couple of days of her period, on Jan 13th and 14th, things became out of control and we had unprotected sex. It again happened on Jan 16th (and on 17th?), 20th, 21st, 22nd and 23rd. Each time we used pull-out method, and as far as I remember I did not ejaculated inside her. Being cautious, I gave her a contraceptive pill (Unwanted 72) on the night of 23rd. Other thing I would like mention is that after Jan 20th my semen became clear, watery, and thin. So probably there might have been less sperm count. The whole situation is now freaking me out. Please help!