What do i do

Yesterday I started my period and my cramps get very bad to the point where I vomit and have diarreah. My doctor says I don't digest well and stuff about my stomach acid. So yesterday I pulled through and conitnued my shift but then my boss told me I had to return in the afternoon to work another shift. I told her I would see if I had a ride (but in reality I wanted to see how I felt around that time). I called in and said I could not make it for the last minute shift I was asked to do. They said okay. But I am still feeling horrible today. I pulled through another day shift but apprently they scheduled me to come back in the afternoon. I am not up for throwing up 3 times from the smell of food (I work at Ihop) and cramps. I am obviously gonna try to get the afternoon off but I feel like since its fathers day, i was scheduled and I called yesterday. That they might not give it to me. I am also unsure on telling them my reason. My boss is a guy so telling him I have indigestion due to menstural cramps is not pretty. What do I do?