Anal while pregnant

Kiera • Sat, Dec 13 • Married April 18th. Trying for second baby :)

I'm 9 1/2 weeks and just stopped getting sick every five minutes and got my sex drive back. My husbands birthday is on Christmas and he wanted to try anal so I bought a toy and lube so we could try it out, we ended up doing it but the next day I had horrible back pain! Why?