If 3 stool samples for parasites have been negative, it is then quite unlikely. There are other surrogate markers on blood tests to check for allergies like eosinophilia
on blood count or IgE levels (raised).
Allergies to house dust mite, animal dander (if you have pets), grass pollens, weed pollens (in asthmatics) must be definitely checked either in the form of skin prick testing or blood test (specific IgE test). A specific IgE to wheat can also be checked although very unlkely.
Do you get these symptoms after eating wheat products everytime? If no, then allergy
to wheat is very unlikely.
and dry skin
can make the skin itchy so keep it well hydrated and use moisturisers.
Long acting antihistamines will help and avoidance measures once the allergies are identified.
I hope that was useful.