My Husband Has Bouts Of Vomiting And Once That Stops

My husband has bouts of vomiting and once that stops usually about 24 hours and then that is followed by diarrhea and very sore and cramping stomach muscles. He removed lactose from his diet and that did not change. This his happens about every 2-4 months. There seems to be no rhyme or reason and what was eaten does not seem to matter.