@dfoster85 - The key word is "preparing." The body isn't really designed for simultaneous nursing and pregnancy, though certainly many women do both successfully. I think it's the progesterone that does it, but you can get more information from the Kellymom website or rom the book "Adventures in Tandem Nursing."
No, there's nothing you can do about it. Because it's a hormonal change, increasing demand (i.e., nursing more often, pumping, etc.) will *not* increase your supply. Because your son is so close to a year, you might ask the pediatrician if he can have whole milk as a supplement. If he takes a bottle, great, if not, time for him to learn about sippy cups! Or he might be satisfied with an increase in his solid foods.
I think you will find that your son will wean naturally as your supply decreases; after the first birthday, when babies start walking, is a sort of window of opportunity for weaning. The benefits of continued breastfeeding are real, but I think having a sibling is even better, so don't beat yourself up if weaning happens!
And congratulations on your new baby!