Just found your post... sorry so late. My daughter has the same problem, to the point she has nearly been hospitalized for it. Prune juice is terrible, but they have come out with a much better version - Plum Juice! It tastes like a combination of grape and apple juice, it is clear, so doesnt have that thick consistency. I know you can get it at Wal-Mart superstores, and Albertsons, but should be able to find it anywhere. Chocolate covered raisins are another great one I have not seen mentioned. Fresh cherries work GREAT as well as fresh appricots. Dried ones work too, but fresh ones will help soften as well. Frosted mini-wheats work great for me, extra large bowl in the morning. Ask your doctor about digestive enzymes as well. My daughter takes digestive enzymes too. here is a link to the ones she takes...
http://www.nutrivene.com/view_item.php?ProductID=11&
Also try a juicing machine. Costco has the Jack Lalane juicer for under $100 and it works great. Juice apples, plums, apricots, grapes, etc, and use the pulp that is leftover to add to your cooking. I found it is really good in brownies! But you can add it to muffin mix, spaghetti sauce, mix in with hamburger meat. The possibilities are endless. These are all safe during pregnancy and while nursing, but if these dont work, e-mail me ... I have an endless list of things to try.
Miralax does help, but it does have a warning on the back for pregnant and nursing women, so I would ask your doctor and use it as a last resort.
And Congrats on the new baby!