PND is specifically caused by pregnancy and childbirth, and many doctors believe it is hormonal in cause, whereas clinical depression is thought to be due to a lack of a particular chemical in your brain - serotonin. Many antidepressants are SSRIs - selective serotonin re-uptake inhibitors - to make sure you aren't re-absorbing the serotonin you have.
PND usually lifts in a year or so, whereas clinical depression may need longer therapy.
I had both - PND and clinical depression which wasn't diagnosed until after my three bouts of PND. I did take antidepressants, and I think they are good drugs - I wouldn't be here without them. But what helped me the most has been a 2.5 year course of group psychotherapy. Basically, the ADs kept me going, and kept me out of the lowest pit of depression until I coiled get the therapy.
Cognitive Behavioural Therapy is also very highly recommended by lots of people, and it is usually a much shorter duration than group therapy.
I can absolutely understand why you don't want to be one the drugs, especially if you are very sensitive to drugs, but there are other options, that your doctor should discuss with you. My layman's opinion would be that the drugs could be very useful to get you out of the worst of things, with the aim of getting you to one of the talking therapies to help you heal. Also, if one AD causes nausea, another one might not - and if they make you feel better, lift your mood, it might be worth it.
St Johns Wort can help in milder cases of depression.
Have you got support around you - people you can talk to, people who will listen uncritically, non-judgementally? Who will give you physical support - help with the baby, making sure you are eating properly, drinking enough, and getting enough rest?
{{{hugs}}} - and congratulations on your new baby.