First, if you start meds it definitely doesn't mean that you are stuck with them forever. After my second was born I developed late onset PPD and eventually went on them (lexapro) and was on them for 8 months. For most people it typically takes 6 months to a year to get the brain chemistry straightened out. For some, though, it may be longer, and could be years. I was able to go off of them very easily and didn't have any problems until my third child was the same age as my second when the depression started. Thankfully, I was able to recognize it this time and went on meds much sooner. For me it makes a huge difference in a matter of a couple of weeks. I plan to stay on them for six months and then go off again and see how it goes.
Going on meds isn't admitting defeat. It is admitting that you know that you and your family deserve better. Depression isn't some sort of personal failure, it is a brain chemistry issue. If you can deal with it in natural ways, that is great, but if you decide that meds are the way to go, don't feel like you are tied to them forever.
Also, I doubt if you are the only person you know going through this. If you belong to any playgroups or mothers groups, I would be surprised if there weren't other mothers there going through the same thing. I have many, many friends with babies and young children who suffer from depression. For us, it is sort of a bonding thing, but I know that for many, they are still afraid to talk about it for fear of being judged by those who don't understand depression.
I suggest you print out a copy of the quiz and call your doctor. Take the quiz in with you because it is a great starting point and will let your doctor know a lot about how you are feeling. It also is concrete so you can't just say, "I'm okay, it's really not that bad. I'm sure it will be fine" which is what I tend to do.
Keep in touch and let us know how you are doing.