Numb/sore hands

Sherre • 26 year old married future momma who can`t wait to see her future baby boy!
I'm 38+1 and like many of you I only sleep on my sides, mainly the left side. I've noticed lately that whenever I switch to my right side and lay on it for a while, my right arm and my hand goes practically numb and it feels sore when I open and close it. It's annoying because I can't sleep only in one position all night, it makes my back hurt and my body feel stiff when I wake up. 
Anyone else have this experience? Know why this is happening?
Thanks for the help!