He can’t stick it in without it hurting

Hi… Idk if this is embarrassing for me to come here, but my boyfriend and I have been dating for quite a bit and like we have been intimate, but recently, we tried doing sexual intercourse as in he would like stick it inside me, but no matter what he did he couldn’t stick it fully in without it hurting like really bad, I’ve tried going on top of him and he tried laying me on my back and no matter what it hurts and it doesn’t get anywhere, do any of you know why this may be happening and if there are any tips of any sort that could prevent this?

(Edit) I thought I should maybe mention, I am a victim of sexual assault and I wasn’t sure if that may pay an impact on anything?