Thanks for the valuable info you had given.I've taken a close look at your question & the reply and come up with the following answer:
The symptoms you are having can be due to a condition called gastroenteritis what you call as stomach flu.Gastroenteritis is the irritation and inflammation of the digestive tract.
Its most common causes are:Food poisoning, viral infections, food allergies, improper diet, and intestinal parasites or bacterial infections.This may last upto several days and a prescription medication may be required.
The most probable cause seems to be food poisoning because of fish you had for dinner on friday.
You can take the following medications:
-Tab meclizine hydrochloride(brand name: Dramamine).This will help you greatly in
stopping the nausea.
-Tab.Acetaminophen for relief from back pain & abdominal pains/cramps.
Watch your symptoms for the next 2-3 days, if still the symptoms persists,then you may need antibiotics & anti amoebic medications to cure this. In most cases,this gets resolved with the above symptomatic treatment.
Hope this helped
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