You are a pain in my butt!!!

Keyana • I'm quirky and in my loving relationship
Like... Literally. So my boyfriend and I were doing anal sex annnd like......... Well it was great and all and it felt good and I love bring fingered there but it was just like... All of a sudden with his penis in me i had this deep pain!!! It was like del in my anus and like in my back and stomach that it hurt so I had of make him stop and this what my first time doing anal and it went so well until that!!! And we want to do it again but I'm kinda scared about that!!! What was that! Has anyone had anything similar?!?