I have been really inconsistent with taking my birth control. I would take an entire pack of Tri - Sprintec and not get another pack for another week or two. But in between time i have not been sexually active. I now the pill sint not fully in my system or at least I do not think it is. I received a pack yesterday and took my first pill this morning but I havent started my period yet. I know my period isnt regualr since I was on/off witht he pills. But do you HAVE to take the first pill on a Sunday or after you end your period? I do not know too much about birh control pills. I just know i dont want to get pregnant, i just had a baby. LOL!!!