During a transvaginal ultrasound how can you tell which side is your left and which is the right when looking at the screen and vice versa for reg one?

Depends : It depends on how the transducer is oriented. By convetion, the left side of the screen is either toward your head or toward your right. It would be hard to know which it was unless you knew what you were looking at.

Left is right: All radiology cross sectional exams are viewed if you are looking at someone laying down from the foot of the bed. So the left side of the screen is the right side of the patients body (same as if you were looking at someone facing you). The ultrasonographer should label the sides with a right or left annotation.