Your help is greatly appreciated.....Employment question during pregnancy.?

ive been employed at a company as a nurse aide for almost 4 years. i am 6 1/2 mos. pregnant and have recently been put on light duty from my doctor due to a condition. my HR lady stated their policy on light duty is none unless you have a work related injury. i know there is other positions in the building that would be lighter for me to do for the remaining 2 months before i take my family medical leave. i even spoke to a director in one of those positions and he said he even needed help bad for one of these positions and that theres nothing strenuous about it. my HR is really trying to do everything so i sign the papers to take my leave now. im meeting with her and the administrator of my building tomorrow to see if i can take another position for the remaining 2 mos i have before my leave. if they deny me this position, do i have a case against them? signing for he family medical leave reserves my job but denies me of pay. im married with a baby on the way and bills to pay.