Sore tailbone?

I'm almost 18 weeks and randomly in the middle of the day, it feels like I have a bruised tailbone. It wasn't like I exercised or slept weird, because it happened right in the middle of the day. I'm also not feeling this baby move quite yet, and I felt my first at 14 weeks. Wondering what thy symptoms sre from an anterior placenta? Wouldn't I have been told I had that by now though if that was the case? I guess it doesn't matter if I do have it, it's a normal thing, but I'm just curious. Also, I've had hip and back pain with both pregnancies, but this feeling in my tailbone is different. It's actually a little to the right of my tailbone.