Asking for accommodation while pregnant

I am almost 30 weeks pregnant and i work as a middle school teacher. I have teaching load of 6 periods per day each 50 mins in two separated parts of the school. Sometimes i need to finish a period in a class that is upstairs on one side of school then go to the next one that down stairs on the other side.

Everyday i get home totally exhausted. Im having this high load bc we have shortage and since other teachers will be covering me when im on maternity the VPA thinks its only fair i take the higher load now, but physically this is killing me.

Yesterday i had the worst back spasm i honestly thought it was contraction. Will it be inappropriate to ask for accommodation?