Pregnant teacher

Right now I’m 23 weeks pregnant and a teacher at a middle school/high school. I do lunch duty everyday and to be honest the kids are little bit all over the place and rough... today there was a fight and wasn’t much I could do except run and find a security guard. Do you think I’m justified to ask for another type of duty or I should just stick it out for a while? All teachers take turns with this lunch duty and don’t want to not be a team player either... but honestly I feel a little uncomfortable being pregnant in the crazy cafeteria.