What Causes Vaginal Bleeding After Taking I-pill?

hi,i had my last period on 10th FEB.,that lasted for 5 days. i had sex with my hubby on 18th FEB,but contraceptive failed so i took an i-pill to be on a safer side. But on 24th FEB i started bleeding.,it was very mild that day and also a bit brownish. The next two days it was like normal menstrual bleeding.,and on the fourth day it was like the 24th. IS this Vaginal Bleeding? If it is so,for how long will it last? Are their any chances of getting pregnant?