What Could Cause Delay In Periods?

Hi there. Basically i'm 20 and female and started taking the contraceptive pill Loestrin20 4 months back. I was very good with remembering to take it and took at rougly the same time each day. However, for two months of this i continued to take the pill without 7 day breaks and now after coming off for a break there is no sign of my period. I'm terrified i could be pregnant but wonder if it could just be my mis-use? Please Help.