MotherToBaby is a great place to learn more about medications, environmental exposures, and anything else you are worried might be a problem with breastfeeding.
Lactation Link offers online courses about breastfeeding from an IBCLC.
KellyMom has great evidence based information
Find an IBCLC in your area here.
Milkology has a bunch of free resources you can use.
You can find breastfeeding support through the Leaky Boob Community, KellyMom, or La Leche League