I was diagnosed with PND when my son was nearly 2. I told the GP that she had a number of choices:
a) take my son away from me
b) put my son on medication
c) put me on medication
I was sort of joking but not really. She said, "Well, let's start with you, shall we?" and gave me HRT. Within a couple of weeks, I couldn't believe I'd said that about having him taken away from me. My son used to "nag" me to death and I couldn't bear it - felt like I was going mad. Once I was sorted out, he didn't do it again. I think my mind was all over the place and he was desperate to attract my attention.
Please see the GP. Just explain to him/her as you have to us. You'll soon feel better and able to cope.
Cut back on your messages and phone calls to your partner. He can manage without them, but if you send the wrong sort, you'll both feel awful.
And about the writing - it's a way of getting into another world, isn't it? It gives you something else to live for. Why don't you, when you go to bed, come on MN for half an hour (time yourself) and then write something, anything, for another half an hour? Write about happy times in your past - your first kiss, your first job, times in school when you'd laugh till you cried. Don't write about worrying things, not at that time of night.