J.B.
Yes, call your doc. Did you breastfeed and are you still? A good friend was fine for about 9 months (when she was breastfeeding a lot) and then as her son ate more solids and she breastfed less, her hormones got all out of whack and she spiraled very quickly into severe PPD. All's well that ends well, but it was a very scary two years for her and she lost everything dear to her (her job, marriage, custody of her child, etc.). Anyway...her case was very rare and I don't say that to frighten you, but we all thought she was out of the woods (she had a prior history of depression so she was at risk for PPD) because she sailed through the first nine months without any issues and we were caught totally off guard by the late onset, but it certainly does happen.
Do talk to your doc - no one knows you like you do, and no one understands feeling "off" like you do. There is no shame in seeking out help and if PPD is the culprit (it can be triggered by a stressful event like death or even changing seasons), there are many proven treatments that will have you feeling back to yourself soon.
Hugs and best wishes to you - listen to your gut!