PPD, or any kind of depression, really, can manifest as extreme anxiety. Some people respond to low serotonin in the brain by getting very very down and slowed down, others by increased anxiety.
There is a great resource, www.postpartum.net
that also has links to providers in your area. There are also links to support groups.
There is also a great book, Beyond the Blues, by Shoshanna Bennet. She also has written PPD for Dummies. You can find them both on Amazon. I think it will comfort you to know that this is very common and it's something that can be very much helped with medication and/or therapy. But you've got to find a therapist that has experience with PPD and PPAnxiety. Many don't. I was diagnosed with GAD after my kids were born because I saw a therapist who didn't "get it". By the time I found my current therapist, who specializes in PPD and PTSD following childbirth, I was diagnosed with both of those. It's hard if you don't see someone who "gets" the PPD part of it and many therapists don't.
Hope you are feeling better soon. There is a biological component to this, and if you think of it in a primal sense, it probably did benefit mothers for millions of years to have these anxieties, it's the way the brain would help you to see things that "could" happen so you could protect your little ones. But in many cases, and in our modern world, this instinct is probably not as needed, though our brains don't know that.
It does get better. Hugs to you.