Having to go back to work :-(

Brittany • Mommy to a wonderful 6yr old boy, 2yr old girl and 1yr old girl.
I've been off of work since jan.6th due to my back problems. I have to return on Monday and am dreading it. Work doesn't know I'm pregnant yet. My ex boyfriend(not the babies dad)  is my boss. He started treating me like crap when he found out I was seeing someone so I can just imagine what he's gunna do now. We have no HR to go to if he does treat me bad. I'm afraid he's going to put me doing a job that could potentially hurt myself or the baby(I run CNC machines) I need my job cuz I'm buying a house. I know there are laws to protect pregnant women but it's hard to prove your case :-/