Just like many of the things that come with pregnancy, sensitive, sore breasts are caused by your changing hormone levels. That’s why they’re a common complaint during the first trimester. Fortunately, once your body gets used to the increase in hormones that pregnancy brings, they should start to feel less sore.
Some of the tenderness may be down to your breasts growing bigger quite quickly, too. During your pregnancy you may go up a couple of cup sizes or more as your milk glands develop and your blood supply gradually increases. An ill-fitting bra can also sometimes be the culprit so ensure that yours is the correct size.