Irregular Periods: Could a Fall Trigger Your Period?

Question
I'm 17.  My periods are regular and about every 4 weeks.  I am supposed to be two weeks away from my next period, but I just got it about 3 days ago.  It came two days after I had sexual intercourse and one day after I took a really hard fall playing hockey.  I don't think it is a result of tearing from sex because I don't have any pain at all.  My question is if my fall may have induced my period.  

Answer
Occasionally you may have "anovulatory" cycles, and may bleed at unpredictable times during your cycle. Don't worry about it. It is normal for your age. Just keep a record of your bleeding. It will get regular so that, eventually, you will have a 28 day cycle (from the first day of your period until the first day of your next period). If you are sure that the bleeding that you had was not due to trauma while engaging in sexual intercourse, you need not do anything. If the bleeding does not stop or remains bright red, you may have to be examined by a gynecologist to make sure that you did not get any tears in the mucosa of your vagina. It doesn't always cause pain, but can cause bleeding. I would also get started on brith control pills, if you are going to continue to have sex. (That will also help regulate your cycle).