Quackers - I am sooo sorry that you feel like this. It does appear that what you are feeling is because of losing your two previous babies. I've been through a similar time myself. I'm not always very good at explaining myself but I'll give it a go! Be prepared for lots of waffle!
I lost my first at 24 weeks in December 2002. Although this was obviously awful, , he was born with alot wrong with him and without going into specifics, he went into such a decline after two days that it was kinder to let him go. We had never cried so much - it was awful, but knowing what we did was ultimatly right - helped.
I was lucky and got pregnant again quickly but once again after having a textbook pregnancy, I lost her at 26 weeks in August 2003. No apparent cause but this time and she was fine. It took awhile for me to grieve properly - I think I kind of shutdown. I tried not to think about it for awhile but one day I kinda lost the plot and cried and cried and cried but boy did I feel better and things were easier.
I now have two memory boxes crammed with mementos. Hospital stuff, pics and everything. I have two georgous photo frames with a lovely picture of them each and I have put them in a position where I see them everyday (if u know wot I mean).
Again I got pregnant within 2 months. Perhaps I should have waited I don't know. Anyway I am now 28+5 and I think especially about my last all the time. I recently spent 4 weeks in hospital (24-28 wks) and at first I felt quite down and tearful as I couldn't get my last out of my mind (I was also quite short with my DH). Like you I kept thinking be thankful you have got this far as should something happen (touch wood) the chances of my baby surviving are strong.
I've bought this simple wooden frame With space for 3 pictures, the bigger of the picture being in the middle. I have every intention of putting a pic of this baby and the others either side and proudly displaying it. I tell people this is my third and my DD in waiting will know she had a brother and sister. I used to say yes to people who asked me with my current pregnancy 'Is this your first?' I don't anymore as in my mind it isn't.
Quackers - you have been a source of inspiration to many. Be strong and hang in there and for one second do not feel guilty about what you are feeling. Your baby will have wonderful mother and father and older DD
P.S. Apologies for going on!