A good resource is LactMed
I took medications while I breastfed for 3 years with no I'll side effects. Most doctors aren't sure so they will say not to.
You might check out the breastfeeding forum too. This is a great question for your doctor--- that's your best source of information. Most docs do a risk/benefit analysis. MANY women need antidepressants after giving birth as depression/anxiety after giving birth and shifting hormones is not at all uncommon. There are safe choices for nursing moms. Talk to your doctor. During pregnancy, they tend to be more cautious. But again, when the risk or need warrants it, they make the safest choice. Best of luck
I had the same question you did because as of today my doctor put me on Zoloft and although she assured me my baby would be fine and it would be OK to breastfeed I'm still worried something could happen.