Left arm "falling asleep" - hurts

Hello
I am on my second pregnancy - 18 weeks , my left arm fell asleep last night
and I woke up in pain and couldn't find a position beside lying on my back
to wake it up again, or to walk it off.
Last time it happened towards the end accompanied with carpal tunnel, it
went away few months after the birth of my son.
This time I still have much more time to go, any ideas of what to do?
Thank you, Ronnie