Microgynon pill and pregnancy?

Bit of advice please, I take the Microgynon 30ED contraceptive pill, which has a 21 day pill cycle and then a 7 day withdrawal in which I have my bleed. I usually don't start my bleed until day 3 of the 7 day withdrawal. I had unprotected sex with my boyfriend on day 2, could I become pregnant? If so, when would be best to test?