Masturbation on stomach

I haven’t asked my doctor about this yet but does anyone know if it’s safe to masturbate while laying on your stomach? I’m 31 weeks and have had a huge increase in a sex drive lately so was needing a outlet when husband isn’t home. Laying on my stomach is the way I usually take care of it. My belly isn’t all that big (yet) so it didn’t seem to be much in the way. And it seems this is the only way I can get a orgasm....so frustrating! Even when I want it so bad and get it I never can reach a orgasm...anyone else have this problem?