Most likely your son is having
Gastroenteritis. Gastroenteritis is inflammation of intestinal mucosa. Most commonly caused due to viral infection however it can be a bacterial or
protozoal infection also. Diarrhoea, bloating, nausea and vomiting are most common symptoms. Its not necessary that each patient has all symptoms.
I would initially recommend you to go for stool routine and microscopy test to rule out the cause of infection.I would suggest you to give him,
Loperamide 2mg sos (as and when required) to stop loose stools.
For cramping and spasmodic pain i would suggest you to give
Dicyclomine along with Mephanemic acid and
Paracetamol twice daily.Your cramps should settle down with it.
A good quality
probiotic like Econorm can be given twice daily for few days.
A short term course of antibiotic and antiprotozoal can be taken after reports of
stool test if required.
Keep Metochlorpromide tablet with you in case he start's feeling nausea you can take it.
Give him a plenty of fluid especially those rich in electrolytes like Orange juice,Coconut water.
Hydration should be maintained.
Keep an eye over his blood pressure.In case if systolic B.P falls below 110mm of hg take him to the nearest emergency department for parentral therapy.
Hope i answered your queries well.
In case you need any further details feel free to ask i would be happy to help.