[header] How to know if menstrual periods have stopped [title] Evaluate the contraceptives you're taking. [step] If you missed a period while on birth control pills, your period may be irregular or absent longterm depending on how you use the medication and your body's reaction to it. [substeps] Oral contraceptives typically come in 21 day packs with 7 days worth of inactive placebo pills. 
While taking these pills, you should have your period. If you skip the placebo pills and go straight into the next pack, you will probably miss your period.