Changed brands of birth control, to one with different levels of hormones. 4 days into sugar pills, and no period. why??

Later in the week?: Its possible your period will come later in the week. Its also possible that you happened to find a pill that doesn't give you periods. If you don't start later in the week, you should do a pregnancy test since this is the first-time this has happened. If it is negative and keeps happening every month, don't worry about it. Best wishes!