I knew it couldn't be. But just asking.
Your boobs arent filling up with milk yet. Your body will not actually produce milk until after birth. Right now they are prepping themselves to be able to accomodate the milk. You might begin leaking a fluid called colostrum tho. They do, however, get sore sometimes when they fill up with milk after birth. You just have to keep up with the time and feed your baby or pump on schedule.
the actual milk wont come in till a few days after delivery but you can start producing colostrum... the size increase is most likely from swollen milk glands and additional fat as your body prepares... not so much filling up at this time...trust me when you do fill up after baby youll know lol but as of right now you can see colostrum anytime through the pregnancy but dont express it or try to stimulate it in any way as that can make it worse... if by chance you start to leak enough that it is noticeable through your clothes youll need to pick up some breast pad... most dont have to worry about this but its better to have some on hand just incase...