Hi I have been like that in points of my pregnancy too. I found that breaking things up into seperate slots and writing things down can really help. Try not to think too far ahead and assume the negative.
I was getting really stressed about money, so I wrote down my budget and researched what I was entitled to, the suprise that I would get some financial help really calmed me down.
Talk to mortgage company about taking a payment holiday if possible.
Babies don't have to cost the earth, I've treated myself to a pram but everything else has been lent to me.
The way I handle my 'can't cope' feelings is that I think that I won't have to learn it all in one day when the baby arrives. In my head sometimes I am worrying about coping with a newborn, a tantruming toddler and a stroppy teenager all at once and I get overwhelmed.
Talk to people - my friends funny stories about their pregnancy/newborn anxieties have really helped me get perspective. One friend phoned her mum at 3am to ask if her baby needed to wear a hat in bed, to which her mum replied do you wear a hat in bed? and hung up :)
I guess you need to take care of yourself too, lots of relaxation, there are some good guided meditation for pregnancy cds around. Just all the traditional stress relievers like a nice bath, lots of rest, cut out caffeine, light exercise can help too.
I am still up and down at times and wonder if I'll ever be sane again :) but attacking the irrational worry from all sides with just a few little things has helped me, hope it will help you xxx