Your body is going through an amazing transformation while pregnant. Not only are you working on growing a little one, but your body is also preparing for when that bundle is born! Your breasts can become sore and/or leak small amounts of colostrum during your pregnancy for these reasons.
Ever since you were born, your body had the components to produce breastmilk one day. During puberty, breast tissue grows and estrogen levels increase. When you become pregnant, your milk ducts spread and grow.
For many women, breast sensitivity caused by these variety of changes can be one of the first signs of pregnancy! The soreness you feel is from the breast growing and creating the pathways for breastmilk (lactiferous ducts). As for the leaking, your body is practicing making colostrum-baby’s first food. Colostrum can leak at any time but it is common for leaking to be more prevalent in the shower or during sex.