Why does birth control sometimes make you miss periods? is it birth control or changes in your body or what?

Hormones contained: Women using birth control pills can expect lighter periods, and sometimes no periods at all- since the hormones in it can really thin out the lining of the uterus. This can even occur with normal pill pack use including the placebo week, not just with extending cycles or doubling up the active pills in several pill packs.

Pill amenorrhea: Birth control usually prevents ovulation, but also thins out the lining of the uterus so that your period gets lighter or stops. There's nothing wrong with that. For many women its a pleasant side effect. However, if you miss your period and your on birth control there is a still a 3-5% chance of pregnancy so check a preg. test if that happens with occasional skipped periods.