Is It Normal To Get Early Period While On Microgynon?

I am currently on Microgynon and am currently running 2 packs back to back. I am due my period next week, but have started today instead, and am wondering if this is normal? I have been on this pill since 2002 and haven't had any problems before. The "period" I currently have is not heavy (more like the end or beginning of a period) but I am slightly worried.I am not taking any other medication, and am 5Ft 2, 10 and a half stone and suffer from asthma but no other health problems.