For 4 years, every month, my sister suffers from severe stomach pain and constantly vomits when her period comes. doctors said it was normal. is it?

SEVERE PMS SYMPTOMS?: THis is very unusual. She needs a second opinion, full exam, pelvic exam and labs. She needs to be screened for GI cause of vomiting. Rarely endometriosis can seed and attache along the GI tract. This could potentially be a cause for severe pain and vomiting during period. Seek a second opinion and get copies of all prior records.