I am so sorry you are going through this. It is the worst feeling in the world, not wanting to be at your job and HAVING to go every day.
I can relate somewhat, I had a high stress job when I was preg with my first but I stuck with it thinking the same as you...I NEED it and there will be no other jobs available cause I'm pregnant. Plus we live in a small town and it is mostly Agro businesses. My husband is GMO for one of the main Grain terminals...so another hit against me nobody will hire the preggo wife of the competitor's GMO! (I was in office management.)
I regret being so stressed during that time in my life, but I will be honest with you, even in hind sight I do not know how I could have done it differently.

(But then again I didn't try anything else either)
Can you maybe talk to your boss and let him know that you are feeling a little overwhelmed and could you maybe get some help until you are caught up again? He/she may respect your honesty and appreciate that you have the best interest of the firm, rather than being too ashamed that you aren't able to complete it all on your own. I can tell you have great work ethic, because you don't want to screw up...maybe your boss will see this too.
Good luck and I hope things get better for you.