C.,
My take is that your change from work to home and your turning 35 may have more to do with it than your pregnancy. I could definitely be wrong but, when I turned 35, I had just moved to a new state and given birth to our third child and all of these factors came together in a way that made me feel much of what you describe. The changes you describe - going from the work world to being a stay-at-home mom at a time of pregnancy and a significant 'marker' in years - again, I could be wrong but these are all factors that seem to say to me, "take it easy on yourself - it will get better."
As for the worrying about your chidren and potential of post-partum, maybe it might help to talk with them. Take it or leave it, but, I am one who believes kids are pretty darned smart - and the more connected they are to their feelings, the better. It's okay for kids to see us cry or fail or fall short or lose our tempers once in awhile or be imperfect - in fact, if we shield our children from seeing how we cope in life, we miss great opportunities to teach them valuable lessons! So, the way I see it is, right now, you've got a golden chance to engage your children and feel great as a parent, in doing so.
Even the smallest ones can understand things if you put them in simple terms. And kids LOVE to love you - if you tell them that you don't really know why but you've had a lot of sad feelings lately and then ask them if that ever happens to them, they will LOVE you for that! Ask them what they like when they feel that way - what makes them feel better? Do they have any ideas that might help you? Tell them you're trying to take care of your feelings - that you're human, JUST LIKE THEM and have feelings that need to come out and be taken care of and that you know, one of the best way of fixing our feelings in life...is to talk about them! Could you be a more lucky mom, than to have two such kind listeners - two such helpful kids?! You might be surprised at what your kids want to offer and how much it can help them, as it helps you, too. Certainly, it won't fix it all...but, I strongly believe they will feel empowered and you will take more joy in their having this feeling, instead of the one that goes with their just watching you cry.
And, likely, you DO need some adult conversation and to find opportunities to take care of that part of yourself. Whether it's through a hobby, a walking workout with other moms or finding a sitter so that you can let Calgon take you away - whatever - you need to make sure you get some of those needs met. Because it is true, you can't nurture others if you're not taking care of yourself, first.
I'll tell you, what I do in my own life is to make sure that once a day there is one item (no matter how small) that is mine - a total, immediate gratification 'fix' set aside especially for me. Something that gives me a sense of either relaxation or completion (or both). Take the idea of doing something from start to finish - I mean, the laundry is endless, as are all the chores of being a stay-at-home mom. At work, you always find something to point to and say, "I did THIS." It's all so...quantifiable! THAT is an important feeling to ensure you get as a stay-at-home mom. So make it a priority. Make sure you have little things you can look forward to and say, "I took 20 minutes and read about X" or "I took 1/2 an hour to exercise" or "I stopped and had tea and wrote a poem." Whatever it is you choose isn't important - it's the feeling you get in meeting a very important need you have as an individual (be it for a sense of accomplishment or just pure relaxation...because you just plain deserve it!).
Finally, a great thing to keep in mind is that you're going to be fabulous for a whole year of 35 - I didn't think so for the first several months (and, generally, I'm not one who gives a darn for what age is on my driver's license!) - but, I was wrong. I think it's just one more of those natural things we women go through - so have a good cry, dig up some faith from within and then go rehearse your next karaoke act while vacuuming that living room!
I wish you many hours of joy with your children before #3 is born - and a great delivery - and a joyous year ahead for you and your entire family!
WR,
T.