Numbnes and pain in upper extremities

I am 23 weeks pregnant. I love side sleeping, however on my right side. I make attempts to sleep on my left, but not only does it bother my hip, i seem to roll onto the right. The problem is that when i end up on my right side, i am awakened with numbness and sometimes pain radiating down my entire right arm. I know this is pregnancy related, just hoping someone can help.me understand why.