I'm miserable.

I'm only just shy of 17 weeks with twins, and I really dont want to work anymore. I LOVE my job and I love what I do...... but my boss is the absolute WORST. We are SO SO SO short staffed, which means I have to do other peoples work on top of my already busy days. I work 12 hour shifts. And I have to drive an hour to work, then an hour back home. I work full time, and its mentally and physically exhausting. I'm trying to stay positive but I just cant..... I live in Canada, and I want so badly to be taken off work and go on short term disability. Its causing me so much stress and anxiety. Last OB appointment he told me he would take me off at 28 weeks at the latest. I just dont know if I can make it that far. I feel really silly...... and I dont think he would take me off early without an actual reason. My pregnancy has been pretty uneventful so far. I just dont know if mentally or physically I can keep doing this. Any suggestions? Next OB appt is at 20 weeks.