Why have I missed my period?

Maggie Reynolds Asked: Why have I missed my period?I got my first period about a year and a half ago and since then it's been irregular. I'm sexually active and twice when my boyfriend and I have had sex in the past month (right after my period) the condom broke. He didn't *** and we stopped as soon as he realized it broke. However I know he always has precum when he gets really horny. Me and my friend usually have her periods around the same time, and hers ended a couple days ago. I don't know how long my cycle is, but lets say its 28 days. If you count your cycle from

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