Is it okay for a pregnant woman to work 10 hours a day standing up?

Okay girls so I’m pregnant I am currently 6 weeks and 5 days. I work as a waitress so I have to work 10 hours a day all week, I have been having severe back pain, I already talked to my manager and they know I’m pregnant but they don’t want me to work half a day the want me to work all day and if I don’t want to they are going to fire me, what should I do? Is it okay for a pregnant woman to be standing all day? This is my first pregnancy.