Is this discrimination against pregnancy?? How should i handle this?

I have been working with a company since being of March and they knowing hired me being pregnant. I worked full time has a contracted laborer then hired me to work part time to complete my 90 day probation. I was originally hired to put away charts and deal with records, since i have been given many various jobs. I can no longer bend up and down to file away everything. A doctors note has been given regarding this. I still am very busy with plenty to do at work. They recently are requesting me to leave on maternity which i can not financially afford. I am afraid they will try to fire me if i do not take my maternity leave. I have never recieved warnings which is in the companys hand book that you recieve 4 warnings for various misconduct before termination. I haven't done anything to diserve a warning nor have i recieved one. They printed me out the disability papers for maternity leave also. I am only 32 weeks pregnant and in NJ the law is 36 weeks for disability. Help