I've read that its a pregnancy symptom for ur shoulders to be in pain. I used to get it a lot in my 2nd trimester
Pulled muscle, pinched nerve, you slept on it funny, you hit it into something. The possibility of whats causing it isn't something we can really say for sure. But as far as to take away the pain tylenol is whats said to be safe during pregnancy. If its night where u are call your doc in the morning if the pain doesn't go away by tomorrow.