To the moms who had PPD, when did you start feeling blue?

I'm wondering if I have PPD, though I am 7 months postpartum and haven't really felt down at all until recently. I thought I was in the clear when I felt fine a few months postpartum, but recently I've been feeling REALLY hopeless and down. Like really, really down, where I don't feel like talking to anyone. I'm wondering if it's the holiday blues, hormones due to weaning, or PPD?

Anyone have any experience with late-onset PPD?