Nausea while standing still?

Erica

I work at a grocery store in a position that’s leading to management, and once in a while my managers will schedule me to be on a register. I’m FINE in all other positions that I work in due to the amount of movement that I’m doing, but the second that I go on a register and I’m not moving, I feel nauseous, clammy, I get cold sweats, and I feel dizzy. Is there a reason for this?? I’m 25w5d pregnant. 🆘 PLEASE!!