Uncooperative boss.

I work in the dental field as a dental assistant .We have two dentists.I am considered high risk due to my age. This is my 1st pregnancy. I work with two doctors and they both have an assistant. I am one and their is another to assist the other doctor. I told my doctor i work with i have to take half a day because I have a obgyn appointment. He said ok do what you have to do.I booked the appointment on a day that my doctor i work with leaves early, so in the afternoon the other doctor is in the office working, she has her assistant to assist her.I also told the other female doctor i work with i have to leave early to go to my obgyn appointment. She told me I have to make my doctors appointments on the day are practice is closed. (She has 4 kids herself).She doesn't want to pay a temp agency for a assistant .I told her my obgyn does not work on Fridays or weekends.I come to work every day and do my job. I felt she was being unfair. My baby and myself health is important .How would anyone handle the situation?I also told her i will be seeing a new obgyn that is open on Fridays after I see the obgyn I am seeing currently until my new insurance begins on February 1st. My other co worker is the office manager she is pregnant also she has took off work to go to her appointments.