Are you only having this trouble when drinking flavored water? or do you also have this problem when drinking tap water.
If you are only having this problem when drinking flavored water then you are reacting to what the manufacturers had added to the water - additives, flavors. These days 'Flavors' are not natural and are created in a laboratory. You could make your own flavored water by adding the juice of lemon, lime or orange (from real fruit).
Have you been seen by an Allergist? It might not be the water.