Itchy flaky scalp and excessive hair loss after eating foods except ( whole wheat ) and the food allergies test (prick & rast ) was negative . why ?

Alopecia and allergy: It is unlikely that food allergy has anything to do with hair loss. Plus both prick and blood test for food are negative so you are unlikely to have ige mediated food allergy. Many things may cause hair loss including androgenic (male pattern) baldness, fungal infection, autoimmune disease like lupus, thyroid/pituitary dysfunction, iron-deficiency anemia... You should talk to your doctor again.

Indirect effects : If one notices an effect from eating foods on bodily functions, it is wise to listen to one's body and avoid foods that produce adverse effects. If food allergies tests do not show effects they could be blocked because of of use of rx anti-histamine meds like desloratidine but the other possibility is that the food grows bacteria or fungi in the gut that produce the adverse effects.