Me breathing and sleeping is better than the baby not getting enough oxygen and me being exhausted.
Unless you think your OB didn't really understand the situation and therefore prescribed you something stronger than what you need / something entirely unnecessary, I would go ahead and take it. You are right to consider whether the cure is worse than the illness, but you are also correct to consider how much you trust your doctor... If you trust her, and if you think she clearly understood your symptoms, I would trust that she has good reasons for it.
That said, if you would like to know why she chose that drug, you should feel free to ask. Be prepared for some degree of delay in her response, since she'll have to relay the message between appointments (and more urgent calls).
At a certain point, it's really a trust issue - I know it's hard to trust someone that much, but that will be what it boils down to...