Calling Out

I'm currently 34 weeks & 4 days pregnant.
I have been calling out of work more and more with each passing week. I'm trying to be responsible, but this last trimester has really kicked my butt. I would love to take leave already, but I can't afford it, and my job is physically draining and long hours (including a nice drive there and back). I've been very nervous about getting fired. What can I do at this point? I feel very stuck...I'm a teacher & if I ever stop working full time hours, I lose my insurance (so I can't even cut down my hours)