I feel robbed

My son is 6 weeks old and I'm still on unpaid maternity leave. I'm a teacher and this whole experience with my job has left me feeling very taken advantage of. Because I teach Spanish my two subs have been less than stellar and I've been expected to make lesson plans my whole leave. In addition to that I am still expected to produce evaluation materials while on leave. Essentially I am working and not getting paid. I know it's not right, but my Union sucks and has told me they aren't going to do shit for me. I'm so frustrated and I just want to enjoy my last two weeks with my sweet baby boy.