I'm making fun of my girlfriend during her worst menstrual cycle
I hope you're joking, why are you making fun of your girlfriend while she is menstruating?
Her cramps are so heavy and she makes funny noises
Your girlfriend is in physical pain and you are selfishly responding by making fun of her. You need to be more understanding and help her to feel better.
It's fun. I'm making her feel better by making fun of her cramps.
I don't think she probably thinks it's fun, you should not make fun of her and take care of her while she's menstruating instead.