I fininshed my pill on friday lst week and still havent started my period?

im on microgynon 30 and am normally as regular as clockwork.so quite worried. I dnt think i coukd be pregnant cuz use condoms aswell. I have loadsa uni wrk on at the mo and are quite stressed cud this have anything to do with it and in the leaflet it ses u can sumtimes miss ur period dont know what to do.please help!