What Causes Fainting,hot Flashes And Vomiting?

hello,my sister is 68 years old and suffers every month of fainting spells,hot flashes,and lately vomitting along with her other symptoms.This happens every month,like a menstruel cycle but she has had her menopause.Every month around the same time she gets these symptoms for 2 or 3 days.they happen just like an alarm clock.I noticed her this christmas,every hr.for about 12 hrs.Every hour on the hour.At the end it was almost every 15 minutes.I almost forgot to mention that lateley her left arm is in a lot of pain.Every time symptoms happen they last around 10-15 minutes.This has been going on for close to 3 years now.She has been given all sorts of tests and have found nothing.This is not fare that nothing else has been done for her case or no other info is given to her.She just keeps on suffering and the heath system is not doing any follow ups .Any info or help would greatly be appreciated.Thank you all kindly.