Worn out!

It is amazing how different my body reacts to work now that I am a baby builder. When I take a few hours to sit down and do computer work, I go to get up, and I realize how badly my back hurts, and my sciatic nerve problem is wow so much worse. Every time I get up I have to grab something for the first few steps so I don't fall down.. :)
Then when I close the store, I have to be up and on my feet for about 6 hours strait walking quickly ensuring the store is running smoothly, and getting put back together after we close. This goes on until about 11pm, then we shut it down, and I usually get home about midnight, or a bit after. I get home, and my legs, and back hurt so bad I cant believe it!
The thing is, is that I actually weigh less now than I did before, so I cant blame it on weight gain. And I am only in my 4th month! I cannot imagine how I am going to cope for 4 or 5 more months!
Then I have been reading a book about having twins, and the advice they give is amazing...I am supposed to gain 50 lbs this pregnancy (wow) and by now should have gained half of that. hmmm. That is A LOT!
The book actually has a lot of great ideas and advice, and ways to have healthy babies, so I am really glad I read it, however one part really freaks me out...they say that if you work a full time job, on your feet or office work does not make a difference, you should plan to start your leave when you are at week 28, and they urge you to leave week 24.
Ya...that is not going to work. I am allowed 12 weeks of leave, and I would use all that before I even had the babies. It just really surprised me that they would say you needed to stop working so incredibly early.
They do say with twins, your uterus at week 24 is actually the size of a single baby would be at 32 weeks, so I guess I can understand if I think about it this way. When I am 28 weeks along, my body will be as stretched and uncomfortable as a single baby at 36 weeks.
So who knows. I am going to have a good talk with my doctor about this at my next appointment.
This journey is nothing like I ever thought it would be. And I just keep telling myself that this will all be worth it, and it will end. They cannot be growing in me forever! I just keep hoping that I am doing what I can to make sure they are growing good and healthy!