How do i get changed for pe class without people noticing my pad?

Privacy: I would recommend changing in a bathroom stall if you are concerned about classmates noticing a pad.

Bathroom...: Perhaps you can change for pe class in a bathroom with the door closed. When you come out of the bathroom, you will already have your pe clothes on. Then, use the same bathroom to change back into your clothes after class. You could also discuss the situation with your school nurse; you are probably not the only one and your nurse may already have a solution for you! you are not alone!