What Causes Irregularities In Menstruation?

Hi. I'm 31, 5foot about 10 stone. Medical history no medical problems but had baby nearly 8 months ago. Was put on the minipill micronor, after giving birth, stopped taking it a month ago, after finished breastfeeding. Not gone back on contraceptive pill microgynon yet, but not had a period yet. Is there a possiblity of getting pregnant in that space of time?