I am a double board certified US doctor and will be happy to help and to give you an answer. Use reply to talk with me, Dr. Thomas.
There are many causes for this, besides pregnancy.
Firbrocystic breast disease: common.
Any thing that imbalances the sex hormones.
Including other hormonal diseases.
You need to see your doctor regardless if pregnant or not.
And go over the list of possibilities with an exam.
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