Thanks ladies, that makes a lot of sense. I'm glad I've got you to talk to - I mentioned how I'm feeling on my 'due in august' thread, and no-one responded except one person, who misread my post completely and helpfully posted 'glad you're feeling better' 
I will mention it to my mw - I tell her everything regardless of whether it's appropriate or not!
And I'll have another chat with DH.
We had a really good weekend, lots of clearing out and rearranging things on Saturday to make the house flow a little easier when Pickle is here. Thing is, DH is really good at being so focussed, and I legged it out of the house as soon as I could, to go and arrange flowers at our church. (I hate tidying!) Sunday was a better day for me as we had family friends and my grandparents visiting my parents, so it was a big family/friend get-together. Felt really relaxed, and able to forget about how I feel when I'm on my own.
When I'm busy, and/or got everybody round me, I'm able to not think about it - I'm pregnant, people congratulate me, DH makes 'yummy mummy noises', and generally I feel good about myself.
I suppose part of me thinks I'm so settled and feel so complete with Mary being here, that I don't want to upset the balance when Pickle is born. I felt rushed into conceiving (I wanted to wait another month or two, plus I was terrified of another EP happening). I know I could have said no, but I was hoping I wouldn't get pg straight away... damn my fertile body!!
The funny thing is, DH was saying last night about how Mary has filled a gap we didn't know we had, and I wanted to blurt out, then why are we having another one?! But I didn't .