Most of the SSRI anti-d drugs are suitable for bfing esp. sertraline (the one I take and have taken since DD1 was 9m/o and have/am bf two other children whilst taking it with no ill effect [anecdata alert!]). Other Anti-ds are also safe for bfing but I have no experience of them.
Ask your Dr to check which ones he thinks is suitable for the kind of depression (PND with Anxiety, PND with OCD, etc etc) you have and check with Dr Thomas Hale's Medications and Mothers' Milk (the textbook for breastfeeding mothers and the drugs they can take) not the BNF (British National Formulary) which is very cautious and doesn't seem to take the latest research into account.
Also, second the CBT rec. it is very good and worked well for my PND-OCD but it is a hard slog (sorry, I wish it wasn't and I could tell you otherwise
).
Lots of HCP will tell you, you will feel better if you stop bfing, and you may well or you may not only stopping will tell you that and by then it might be too late to restart. What I found that kept me with my children was bfing them. It was the only thing I could do for them that no one else could. Bfing made me their mother when I would have given them up and done something stupid.
I had PND-OCD which centred around preventing harm from befalling the DDs - unfortunately a 'friend' put in my head that bfing was harmful past 6m (which it's most certainly not but that played on my mind a lot) but bfing helped me bond with my babies and kept me with them IYSWIM.
None of these comments are a judgement on mothers with PND who chose to ff, just what I found in my situation to help so please don't think I am judging what other mothers may/may not do.
I really hope you get some help whether it is pharmaceutical or talk therapy or both. Good luck and be kind to yourself.