What can cause a woman to miss her period after taking birth control pills?

Multiple: If you have just started bcp, it can take several months before your cycle becomes regular. If you have been taking them a while, any change in your metabolism can change your cycle. Examples include significant weight gain/loss, thyroid problems, diabetes. Just having new stressors in your life, like a family death, relationship change, or tax time can alter your cycle. See doc if it persists.