What Causes Chronic Diarrhea And Vomiting?

I recently traveled to Scotland and returned to the US on June 25th. Two days later (June 27th) I had an episode of violent vomiting and diarreha that lasted a few hours. Afterwards I felt a bit tired and weak but I ate crackers and drank gingerale for a few days and felt better. Five days later (July 2nd) the same thing happened. I was violently ill for about an hour and then, careful what I ate for a few days. I thought it was all over, and perhaps just gastroenteritis, though I am always careful about washing my hands with antibacterial soap especially before eating. Now on the 22nd of July, it happened a third time. Violently ill for about an hour, and now still feeling I should stick to a bland diet. In each case I vomit to the point of dry heaves and have water diarrhea at the same time, forcing me to vomit into the trash bin. As soon as it is over I feel tired, but fine. No fever, but I do feel cold when it happens. No stomach aches, or abdominal pain. I have had some headaches lately and have one this evening. I do suffer from migraines, and have issues with neck pain when I sleep. Though it does seem like I have had more headaches recently. The only medication I take is Estradiol .5mg once a day. I had a physical before my trip to Scotland in June and all of my tests came back normal. I did discuss going off of gluten as a trial at the time of my appointment because I had been on a low carb diet and was told I should add more whole grains back into my eating habits but I found whole wheat made me feel bloated. I have had gastroenteritis before and this does not feel the same. When I had that I had horrible stomach cramps and the vomiting and diarrhea lasted about 12 or more hours. These three episodes have come on fast, I feel nausea for about a half hour before getting sick. I then get sick for 1-2 hours and then both vomiting and diarrhea stop. Do you think that I may have gotten an amoeba or parasite either in Scotland or from someone on the plane?