RosieIrene,
Lots of hugs. No one does manage, everyone just bumbles through the okay parts and staggers through the bad bits. I think everyone feels isolated, because the likelihood of there being someone in your department with whom you are friends and who is in a similar position to you is about zero.
I think the thread has gone off on some tangents, but I would just like to say I am thinking of you. I started a similar thread in January, when I was very stressed at work (a city law firm) and suffering from bullying bosses. The support I got on MN was helpful. Since then I have done the following, which have helped:
I saw a maternity coach - basically an executive coach with a sideshow in executive women - she helped me understand what I needed to do to turn my crazy situation into a better one. Some law firms hire these independent people, some don't, but I think they are useful because they are so tailored to the women in the city. www.maternity-coaching.co.uk/
Then I applied to have one day every other week off. This is sufficient to give me a bit more time to be with my DD, but not so significant that I am seen as part time, with the negative connotations of that at my (not very supportive)firm.
Then I thought seriously about whether it was the job, the tiredness, the expressing at work while trying to read contracts at the same time, and all that, and tried to isolate the particular elements that made the combination impossible. I concluded that it was my bosses and their views, but I am sure that this is different for everyone. I have since resigned to go to another city law firm with a reputation for being family friendly and flexible.
Good luck, I think it is all so hard, and some weeks it feels like you can do both jobs well, sometimes it feels like you can do neither, and then you can also start to wonder where the "you" is. It will get better.