Job and pregnancy

I work in the medical field and I am pregnant. I have my 1st prenatal appointment coming up next week. I told my job about it and they are giving me shit because it wasn't 2 weeks in advance. (My dr is only there certain days). My managers literally brought in HR (which is their friend) just to tell me that I need to tell them 2 weeks in advance and it has to be on days that I don't have clinic. My doctors office are the same exact hours of the clinic I work for. Told them that its not possible. They told me that they don't want to pull people to cover me because I have appts. So now I am stressing because it makes me feel like I can lose my job. But I don't want to but my unborn baby at risk due to stress from this job and these managers! Advice anyone?