Weird butt pain?

I'm going to my doctor tomorrow, but over the phone as of right now they arent sure what it could be. So when I lay down even if it's a soft surface there's pain right at the top of my butt crack . I think it's called the coccyx? It hurts at times when I'm not laying on it like on my side, or when I apply pressure to it. I dont remember doing anything that could have injured me there. Doesn't hurt when I put on a thong or remove it , doesn't hurt during sex, and doesn't hurt when I'm just standing. I'm stumped. It came out of no where. I want to be able to sleep on my back again. I hope the doctor figures this out, I've been taking ibuprofen , but no pain relief.