Frustrated and don’t know what to do

I work as a child welfare social worker. It is required that we work on call. This is on top of our other duties from 8-5. We get kids who hit, kick, punch, slap, spit on us, pull hair, etc. If we work 8-5 and then are on call, we could be out until 12, 1, 2 am and then have to be back up by 5 am. Then work 8-5 again. No sleep. Aggressive kids. Stress. I turned in a Drs note stating I can’t do on call, but my job wouldn’t accept it. I’m 17wks5days. I don’t know what to do. We’re supposed to do on call once a month but I feel like it’s unsafe. Ugh!