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I am a double board certified US doctor and I will answer your question, which I think is: could you be pregnant. Yes, but unlikely.
A change in your period is a reason to contact your doctor.
Changes can be, as you have stated, pregnancy.
Other problems can be at work
Other medical problems
Liver or kidney problems.
weight loss or gain
a resetting of the cycle due to medications, hormones, etc.
Hormonal influences are the most common.
If you are really concerned about pregnancy, the home pregnancy test is accurate when your period is due.
A blood test does not fail.
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