Work place issues

I work at a grocery store which has its own gas station. BEFORE I was pregnant I trained for the gas station and was told I would only be covering breaks and lunches. However that NEVER happened, after training I had only been down there once or twice.

But now that I'm PREGNANT and I have turned in a doctor's note saying I should NOT BE working down there due to the fumes. I have been scheduled down there EVERY SUNDAY and when someone calls in and I am here they give me NO OPTION it's go down there and cover, even if it means staying over my shift or go home.

Is this even allowed? I came in today and was told I won't be working the self checkouts instead I will be at the gas n go. & as soon as I mention my doctors note they ignore me and walk away? What can be done about this? I'm ready to put my notice in and leave, I feel like that are putting my baby in danger! HELP.