Am I being too sensitive about this?

So I'm currently 32 weeks pregnant. I'm a nurse and I work in a plasma center. I do get a 15 minute break roughly every two hours, but sometimes we get really slow periods where we have no donors. During that time, if there is no other work to be completed, I'd like to be able to sit down at the front desk. We used to have a chair there for that reason, but recently management has taken it away and said no one is allowed to sit down. I have been scolded multiple times for sitting while we are slow. I'm not sure if I'm just being a big baby about this and should suck it up lol. Any thoughts?