Can an employer require an employee to stay over their scheduled time?

When I was hired, nothing was said about having to stay 30 minutes or more after my schedule said i was to be off. Before I was hired for this job (fast food restaurant) I informed the lady interviewing me that I had a three year old for which i have two babysitters for, one being a friend who works and one being her grandmother. For a while things were great, then the employer fount out I was pregnant, which I did not even know about until after I was hired that I was 5months along, anyway, suddenly they seem to be pushing more and more work on me, which I do not mind as long as I am given time to do said work. Unfortunately now they are not giving me enough time, they want me to do an hours work in 5 minutes, sometimes they assign me a task right at the time I am scheduled to be leaving. This would not be an issue, except on the days I have a set time to pick up my child and I inform them of this, even wrote on the crew schedule the days an the time to which I could work to. Such as ?-11:00 letting them set the start time, and the days i have no time restrictions leaving open. So then they started to only work me on the days I need to be off at a set time, cutting my hours from 35 to now barely 15 a week. I have no ideal what my options are other then to look for a new job, since all my attempts at coming to a compromise with management has resulted in the things getting worse. Is there any legal way to deal with this, or am I going to end up loosing my job over this. Cause its becoming very clear that they want to break me with the way management now talks to me. Please help if you can, thank you for you time. Faith