What Caused The Delay In Menstruation?

Ive been taking microgynon 30 3d for 10 years. I am 26, weigh 9stone 13 lbs and am fine medically. I double back my pill occassionally and did it last month. Normally when I do this everything is fine the following month. This month I started the break on the Saturday and didn't come on my period until the following friday, which normally I get it on the Monday night. Is there any reason for this delay? I am due to start my next packet tomorrow.