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Thank you for your question, it is my privilege to be able to help you.
Occasionally even women that are regular every month may just have an early period. Stress, weight loss or gain, medications, a new exercise regimen, or various other things can cause it. Most of the time, we never quite figure out why it happens. I doubt that you are pregnant, but i suppose it is possible that this was a bleed in early pregnancy. However, based on your description, it doesn't sound like it. It can't harm to get a home pregnancy test, but to be honest, I don;t think it is necessary. If your periods do return to normal, don;t worry about it. If this pattern continues, you should see your doctor to figure out why your cycles have suddenly become shorter.
I hope this was helpful to you. Good luck!