I've been taking prescription prenatals for about a month now (Nestabs), I was also taking folic acid for about a month prior to starting the prenatals. Ever since being on either of these, my breasts have been extremely painful and swollen. I've got up a cup size - had to purchase a new bra. They are so sensitive that the slightest graze at times can be incredibly painful for me. It's a constant pain too, not just the couple days before my period begins.