Ovranette(the pill) expiry date?

I'm on ovranette and my friend had a spare pack from when she was on it a while ago, im taking them now but didnt realise they dont work after the expiry date. The last pack i took said March 13 and they're the ones my nurse gave me THIS YEAR, the ones my friend gave me say Nov 12, are they out of date? And i've had unprotected sex whilst on them, and had unpro sex after missing them also, could i be pregnant and what does the expiry date mean? when did they expire?