Horrible pain in left side

Savannah

About every month I get a horrible pain on the left side on my body. This occurs almost every night leading up to my period starting. It is literally like the worst pain ever. I usually don’t sleep for this week and keep hot pads ready. Heat seems to be the only thing that helps. I also will lay down in the shower and let that run over the spot that hurts. Does anyone else deal with this or know why it does this.