Try eliminating all foods that contain aspartame from your diet for 1 month. Document on paper any headaches with date and time. Also, document when your menstrual cycle starts and ends. Hormone levels can cause fluctuations in not only headaches but other physical reactions too. Reintroduce 1 aspartame-containing food every 3 days. Continue to document every headache so you can compare headache frequency and whether or not it increases with eating foods with aspartame.
Since you were on vacation, your absence of migraines may have been due to the lack of stress in your life. With the variety of foods and beverages a person eats during a day, it is very difficult to pinpoint one specific food as the causative agent. Try the above elimination plan to see if aspartame is really the cause. Contact the NutraSweet Company in Skokie, Illinois if you think there is a relationship between aspartame and your headaches.
The Center for Disease Control in Atlanta did some studies of physical complaints and the use of aspartame. After extensive interviews with those persons having complaints, found no clear-cut relationship between physical complaints and ingestion of aspartame.