Category D or C are pregnancy categories and not lactation categories-
I am going to get on Cymbalta while breastfeeding myself soon and Xanax can also be taken while breastfeeding.
The warnings you saw on the medicine are on ALL medicines and is just a CYA move by the pharmacy and drug companies and not a true reflection of the drug's safety during pregnancy or breastfeeding.
Drugs are almost always passed on to a child at a much greater rate in utero than while breastfeeding.
Cymbalta is listed as an L3 (safe) but has limited information about it. Some does get into the breastmilk but the baby would get 0.141% of a dose and it appears that the amount of drug that does get into the milk is not able to be absorbed by the baby. Based on that I'd say that it seems much closer to an L2 (safer).
Xanax is an L3 as well but for a baby of 6 months of age and who is also getting supplemented with solids/formula it should be fairly safe to take on a regular basis.
If you have further questions about medications that are safe for breastfeeding check on Kellymom.com, search within in the the book Mother's Milk & Medications by Thomas Hale on Amazon.com, or check Dr. Thomas Hale's Breastfeeding & medications forums. Dr. Thomas Hale is the world's leading expert on lactation pharmacology and if he says a medicine is safe to take while breastfeeding it is.
http://neonatal.ttuhsc.edu/discus/messages/43/8008.html - Discusses using Xanax and Zoloft while breastfeeding. Zoloft is considered the safest antidepressant for breastfeeding mothers to take. His main concern was the addictive properties of the Xanax for the mother but as long as the Xanax is short term until the Cymbalta kicks in, and only for emergencies after the short term period there shouldn't be a problem.
Considering how important breastfeeding is for both your health and the health of your baby more doctors really should support and try to preserve breastfeeding relationships as much as possible. Yes a well mother is important but too often women are given bad information about nursing and medication. Plus there are a wide variety of medications safe for nursing mothers who need treatment for anxiety and/or depression.
http://neonatal.ttuhsc.edu/lact/medicationforumspage.html - Dr. Hale's breastfeeding & medication forums
http://www.kellymom.com/health/meds/aap-approved-meds.html - Short list of AAP approved medications to take while BFing
http://www.kellymom.com/health/meds/antidepressants-hale1... - About anti-depressants and nursing