Your boobs are a good barometer for what's going on in your body. An early sign of pregnancy can be sore, swollen, tender breasts... but then again that can also be a sign that your period is about to start.
You body begins preparing for the birth of your baby as soon as you fall pregnant. To get them ready for producing milk, the hormone increase may may lead to swelling and tenderness. Nipples can also become more sensitive and can feel unusually sore.
Though it can often be confused with breast tenderness experienced before your period starts, sore boobs is one of the key symptoms of early pregnancy.