You're not a complainer! You're exhausted!
On some level, we all go thru this, although you have extra demands because your husband isn't around much on a helpful schedule. You absolutely MUST take care of yourself! It doesn't matter whether the people at work "get this" or not - just take the time! Family leave is a guaranteed right - by law. Don't worry about helping them understand or trying to defend yourself against accusations of "wimpiness" - I guarantee most of them couldn't do half what you are doing! I wouldn't engage in too much debate or too much explanation of why you need it - you just do it. Get your doctor involved if necessary - the emotional stress and lack of rest cannot be good for you.
You absolutely must get some rest, and some sleep - they are different things and you need both. Can your husband take on some of the bill-paying or other tasks that don't have to be done at home or at a particular hour of the day? Can you just forget about household chores like vacuuming and let it wait? Can you afford to drop the laundry at laundromat and let someone else wash/dry/fold? Can you afford one of those supermarket shopping services, even just for a few months? How about all those relatives and friends who say, "Let me know if I can do anything" - or did they appear during the first pregnancy and disappear this time??!! Are you sending out vibes to everyone that you are super-competent and you don't want to admit you need a break? Can you ask for help?
You need time NOW as well as when the baby is born. If you do leave work for a while, consider leaving your child in daycare or whatever, on the same schedule (or at least a partial schedule), so that you actually REST - you may need to sleep in the day time now, since it's hard to sleep 8 hours in the last month of pregnancy - no comfortable positions, the baby keeps moving, and so on. And your child needs consistency and stability. You need to be able to read a book, take a nap, go to a movie, have lunch with a friend, or just veg out. You deserve it!
You are the most important person, both for the sake of the child you have and the one you are expecting.