What Causes Irregular Menstruation And How To Treat It?

Hi iv Been on the mini pill for over 8 month s now but in January I got my period on d 17th and had Intercorse wit my partner on the 22 which was day 5 of my cycle I bled      for 3 weeks after but was due my february period on d 14th of feb  i only finished  bleeding a week be for my feb period .it is now the 3rd of march and I don't have a period . Is it normal to bleed for so long one month and not get a period d next month ? I have always takin my pill on time exactly d same time evert day or should I b worried