Please give me some advice

Hello I am shift worker and my manager has been giving me only one off day and all evening shifts (2:45-11pm). My work requires me to stand 8 hours straight which has been really tiring specially with overtime. I am 22 weeks pregnant. Last week i talked to my manager saying that I can’t have overtime anymore and I would appreciate some morning shifts. But he become really angry said as Supervisor i should be working overtime when we are busy and shortstaffed. Then he offered me to resign if i can’t work overtime. Today he made next week’s schedule and I am not there. I didn’t plan to resign or anything I just wanted regular 40 hours a week and some morning shifts? What should i do? Can they force pregnant woman to work overtime?