I'm glad to know this! Thanks ladies!
Sex on your back is fine. I'm pregnant with my 3rd and with all pregnancies have had sex on my back right through until the day the have been born.
No you're not supposed to sleep on your back after 20 weeks. Sex is fine on your back.
I've always been told you should not lie on your back after 20 weeks. Maybe ask your doc?
Sex is fine. Do it in whichever position is most comfortable.