Hi thanks for asking question.
You have eaten outside food.
So you have
gastroenteritis by that food.You can have viral or bacterial infection of stomach.Do your CBC and stool examination.
Accordingly you may need antibiotic like cefixime or oflixacin and ornidazole.
Meanwhile take omeprazole for few days.
Drink more water.Avoid spicy food.
Avoid smoking.
For few days take small meal at frequent interval.
Avoid excess tea and coffee.
Second you have to rule out
parasitic infection like giardiasis or amebiasis by stool examination.CBC can show
eosinophilia.If it comes positive
metronidazole or
albendazole may needed.
If still cause not clear go for ultrasound examination or endoscopy.
Take cooked oatmeal that is good herbal remedy.
Take fried food very less for few days.
I hope you will recover within few days.
Dr.parth