I dont know why my eczema is flaring up even though i am not eating anything i am allergic to and taking antihistamines?

It happens: Eczema often flares in unpredictable cycles. Weather changes, diet, stress, other health issues have all be considered as triggers in some people. If you are not happy with your level of control work out a eczema management plan (write it down) with your primary care provider that lets you add or delete additional treatments during flare ups.

Eczema: If atopic (allergic) Eczema, may not be related to something you eat, however something in environment can trigger symptoms, atopic eczema is called asthma of the skin. Antihistamines aren't the cornerstone of treatment, skin care and topical treatments as steroid creams/ointments or other newer creams can control it. Better see an allergist / dermatologist for management, good skin care 4 now

Normal: That is part of the normal cycle. At times even doing "everything right" can still cause flares.