It is likely that you are suffering from a generalised acute urticaria
If there is no fever, abdominal pain
or breathing trouble then the situation is not that serious, but apart from long acting antihistamines like allegra, you will need corticosteroids
to overcome this acute episode.
Please see your doctor regarding this prescription.
There are certain drugs that can do these reactions like pain killers (NSAIDs) or aspirin or blood pressure pills, so ensure you let your doctor know if you have taken any of these prior to this event.