When pregnant how fast do your boobs grow. i went up a whole cup size and im pretty sure im only a few weeks along?

There is no: specific way to predict this. Congratulations.

Can be fast: Your breasts do not fully mature until your first pregnancy. This final maturation process during the first pregnancy can produce quite a bit of growth. In addition, pregnancy itself makes your breast get larger. There can be a lot of growth--especially during the very first pregnancy. How much is different woman to woman. Best wishes!