Taking medication is a very serious step. In some cases, medication may not be warranted. However, especially when there is severe depression, anxiety, bipolar, or psychosis, medication may not be a choice, but rather a necessary decision in order to be out of, or prevent, a crisis.
The good news is that there are credible resources that you can look to for information, so that you can make the most informed decision. The other good news is that it does not mean that you cannot breast-feed or that you will (for sure) cause damage to your baby by taking certain medications. The harder news is that information is not always black and white. There may be risk involved. There may be a time where you are not 100% sure, but it is clear that the benefits will outweigh the risks. Here are some resources where you can find research-based information:
http://www.mothertobaby.org: a service of the non-profit Organization of Teratology Information Specialists, is dedicated to providing evidence-based information to mothers, health care professionals, and the general public about medications and other exposures during pregnancy and while breastfeeding. (Copied from their website). This website has a ton of information, as well as toll-free numbers to call for more support.
http://www.infantrisk.com: By educating healthcare professionals and the general public alike, we aim to reduce the number of birth defects as well as create healthy breastfeeding relationships. This website provides great information, and also has forums online for questions.
http://www.motherisk.org/women/index.jsp: this website has a page for both parents and providers. It also has several various toll-free helplines not only about medications but also about things like morning sickness and substance abuse.
http://toxnet.nlm.nih.gov/newtoxnet/lactmed.htm: I really really really like LactMed. However, the information (A medication database) can tend to be more scientific, so if that makes your brain feels like mush, then don't use this website. It does have an app that you can also download onto your smart phone or tablet, so that may come in handy.
The decision to take medication during pregnancy or while breast-feeding can be very daunting. Knowledge is power. If you must read other information aside from what your doctors provide to you, make sure that it is coming from a reputable source. All of the above, in my opinion, fit that bill.