Hey! -
I masturbate by humping my pillow all the time! Sometimes, I hump the bed, or my stuffed animals, and have the best orgasms. From your description, I think I hump my pillow the same as you - I lay face down in bed with my pillow underneath me, and I buck back and forth on it to rub off. I was more than a little concerned while pregnant that if I kept masturbating on my stomach, I might harm our baby. But I was assured by my obygn that the walls of the uterus would protect our daughter. After abstaining out of fear for weeks after learning I was pregnant, I went home with my husband and made myself have some of the best orgasms I've ever had humping the bed!