S.H.
Congratulations!
Well, just being pregnant, you will get fatigued.
As for falling asleep, I think you just have to tough it out... and do NOT take anything, herbal or otherwise, because you are pregnant. Or unless it is COMPLETELY approved for pregnant women. And ALWAYS, tell your OB/GYN of any concerns or questions.
Perhaps, do yoga, or deep breathing... this helps some women to relax...
All the best,
Susan