I Don’t Know What To Do..

My boyfriend treats me differently if I don’t wanna have sex. Last night, I was staying over in his house and I started my period. I had cramps and overall, I just felt unwell. I always know when he wants to have sex so I explained to him that I didn’t feel too good and I didn’t wanna do anything that night. He just acts really moody and quiet. He treats me differently in general. He guilt trips me and asks ‘is it me?’. Every time, I give in and I have to force myself to have sex with him to keep him happy because I know he’ll get a bit pissed off if I don’t do it.