Bristol Palin Is Pregnant With Baby #3

Bristol Palin has bun #3 in the oven ... which means the honeymoon is officially over for Bristol and her husband.

Sarah Palin's oldest daughter is expecting her second child with Dakota Meyer. They just got married 6 months ago, and Bristol told "Entertainment Tonight" she's due in the Spring.

Do the math and it's clear these 2 work quickly.

Bristol and Dakota already have 1 child together. She, of course, also has Tripp with former fiance Levi Johnston.