D.W.
It's OK to take products that contain diphenhydramine (Benadryl's active ingredient) during pregnancy. I had to use them through both of mine. Insomnia is an issue beyond pregnancy for me, so I had to verify with my OB/GYN that it is safe.
Diphenhydramine is the active ingredient in Tylenol PM, Unisom, etc.
I'd ask your OB before starting to make sure they give their blessing based upon your medical history. But, it was my saving grace. Because I had sciatic nerve issues, I chose Tylenol PM.
Good luck!