Also depending on where you live you can look up a local la leche league and they will be able to help. I believe they are a free service as well. You hospital may have lactation consultants to help also. As far as vitamins just continue your prenatals. If you have issues with supply there are some options you can look into but don't try them until you have been nursing for a few weeks and see how it goes. I tried nursing with my son and I gave up way too easy. Turns out he was just fine and didn't need to have a supplement of formula the hospital just had me freaked out. I just needed to nurse him more often than what they told me. If your baby wants to eat every 30 minutes nurse. If baby wants to eat every 2 hours nurse. Let baby make their schedule not you or anyone else. Good luck!
All you need to do is once baby is born drink plenty of water, every time you put baby to breast ensure you drink at least 1 large glass of water, breastfeeding on demand also ensures that your body produces enough milk for bub, you can also keep taking your pregnancy vitamins and make your diet as healthy as you can, remembering that some things you eat can affect some babies, so I would keep juices and gassy food to a minimum for at least the first 6 weeks
I don't know about vitamins but my on told me with my first to drink alot of milk but not to worry to much about it because my body will know when its time to make the milk and he was... right anytime a baby would cry my breast would start leaking crazy how your body just knows lol I hope it helps if not just double check with ur ob good luck and Congrats your lil one is almost here