Tailbone and butt?

Amanda • 24 yrs old. Mommy to a beautiful 3 year old he is my pride and joy. And now we are expecting our 2nd on july 25!
I am 15 weeks pregnant and for the last two months I have had horrible pain in my tail bone and now one side if my butt hurts too. Anyone know if this is normal. I had a case of vanishing twin syndrome but everything else has been healthy w the remaining baby.