If she is a virgin, she is not pregnant. Because you are so young, I am guessing that she is, too, so it is possible that her periods are simply not "regular" yet. That doesn't usually happen until a girl has been menstruating for maybe a year. Also, if she has a very low amount of body fat due to extreme dieting or if she is extremely athletic, that could also affect how frequently she gets a period. I have a sister who is an athlete, and she has never had a regular cycle.

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