After reading the other responses regarding post natal depression, I thought I would add my experience. These wacky hormones are very confusing.
My erratic, flooding, spot all month periods began when my youngest was 14 months. In hindsight, I was very emotional too. I attributed everything to hormone fluctuations from weaning, even though my periods had returned regularly at 6 months.
Things settled for a few months then went wild again. This is when the gynecologist first mentioned perimenopause and ran tests to rule out cysts, fibroids, etc. At this point I was still sane and happy.
A year later, I lost my mind (or I felt like it anyway). At that point is when my gp found my FSH level to be very high, and felt confident confirming it is menopause.
My purpose in telling all that, is to say that it really doesn't matter if it's post natal depression or perimenopause. I believe it is your hormones. Most likely your body is trying to find balance after pregnancy and birth, while trying to transition into menopause. It's a combo from hell, I know. As the others have said, don't give up. Hopefully some doctor will have some kind of relief for you, but even if not, keep going. Your body will eventually find the balance. That's what I'm counting on for me anyhow. Good luck