I only do that much because I am doing my PhD and the work is always there waiting. The less work I do the longer it takes to finish. I don't get paid much as I am on a scholarship (my hourly rate works out to be around $7 a hour - ouch!) but I tell myself it is worth it in the long run.
I am the first to admit that I simply couldn't do it without my DH. And being pregnant as well wouldn't help your energy levels.
My only tips would be to ignore things that really don't need to get done (e.g. ironing). Do bulk meals so you can cook four nights worth in one go. Cut back on any spending that you really don't need to reduce how much you need to work. And I guess just try and remember that it won't be like this forever! Can you adjust your current job to make it easier (e.g. less standing or the option to work from home). Big hugs to you. You must be exhausted poor thing. Having your little one spend time with his extended family is great for him though.