One sided back pain??

I’m almost 12 weeks pregnant with my first baby. This morning, I noticed a pain on the right side of my lower back. Not a sharp pain, just like a pulled muscle feeling. But i know i didn’t pull a muscle. It’s constant but not unbearable. I called the office and they said not to worry unless I’m bleeding. I’m not bleeding but I know miscarriages don’t always have to have blood. Anyone have experience with this or know what it could be?