So I think I have pmdd

Literally idk what to do. I’m 19 and my fiancé won’t listen to me he just tells me doctors make up stuff like this to make women think they are crazy and want to spend the money on prescriptions to fix it. What am I supposed to do. I made a doctors appointment to help figure all of this out but I’m like 99.999% I’m right about this. Please send all the help and advice my way.