Thanks for writing in.
The condition you are suffering from can be urticaria
It can occur after some food intake like in your case.
Proper examination KOH scraping,patch testing may be required for diagnosis.
Avoidance of particular food like pizza ,pinapple in your case will be helpful.
Patch and prick test for allergy
will help in knowing the allergens.
Consider visiting your GP or dermatologist
for proper diagnosis and treatment.
You can take tab.Zyrtec for itching till you visit a doctor.
Hope this helps.