I still have food-related problems even though my allergy test showed negative results. How can that be?

Intolerance? Approximately 20-25% of people believe they have a food allergy, when in most cases it is an intolerance. Strictly speaking, 3-5% of children and 1-3% of adults have a true food allergy. Regardless, if symptoms are consistent after ingestion, the food must be avoided and a visit to physician is warranted for further work-up to ascertain the correct diagnosis.
It depends... Many food reactions are not strictly "allergic" or immediate, life-threatening type reactions we understand well. A world of food intolerance (not life threatening, less immediate) exists that is poorly understood. The best teacher is often experience in the world of food intolerance as so few helpful tests exist.
?intolerance. Allergy symptoms sometimes are an intolerance. Try avoiding the suspected foods and monitor your symptoms. Then ...If symptoms are not severe in any way then slowly try a little of one food at a time..And see what happens. Then if unsure. Discuss with the allergist.
Not an allergy? Food intolerance is more common than food allergy. Lactose intolerance may be the cause of 50% of all complaints of abdominal pain in children. Its possible to have false-negative skin or blood allergy tests. Elimination diets are often the best way to diagnose food allergies & food intolerance. You may wish to return to the physician who performed the original tests or seek a 2nd opinion.
It depends... More than likely as others have mentioned you are experiencing either 1) inaccurate testing results or 2) food intolerance and not technically an allergy. There are many books in the alternative medicine arenas that describe reactions such as fatigue, irritability, GI upset, etc that are not as obvious as rash, hives, or diarrhea. It would be wise to keep an agressive food journal to help.
Inaccurate tests. Not all food reactions are caused by allergies (one may not digest lactose in milk or have arthritis from nightshades, but this is not allergy). Food allergies can be mediated by ige, g or a antibodies and most tests only check for IgE antibodies. The gold standard for food intolerance testing is to totally avoid the suspect foods for a week or more and then eat the food and see how you react.
Inaccurate tests. Blood tests for food allergies are known to be inaccurate, both with false-positive and false-negative results. In fact, up to 20% of people with a known food allergy may test negative by blood. Skin testing is much more accurate, but still not 100%. An allergist can preform these tests and even "fresh food" skin tests and observed office challenges to more accurately determine a true allergy.