[Always *]

No, don't risk it. As a stranger on the internet I do not feel comfortable with telling you that "carefully just once" is ok. Not if it goes against a doctors advice, your OB knows her stuff. I know it sucks, but you'll have to, er, restrain yourself. If you are totally losing it then that's when it's time to talk to your OB again and ask her if there's any way you can manage it without actually, well, doing it. Like ask her if it's ok to masturbate (and emphasize that you won't go to the point of having and orgasm). But if she says that the risk is to great I'd hold off. This is one time when you might want to "suffer in silence" because the risk is so great