Missed period? Or normal side effect?

So I been taken Birth control for about a month now and so far my cycles have been a little off but normal. I was scheduled to have AF arrive on Monday of this past week, but surprisingly she did not show. I tried not to worry to much maybe it was miscalculated, but almost a week has gone and March is just about over. I plan on taking a pregnancy test but my question is is if this is normal for people on birth control or a missed period?