Hi.
Have you not taken any medications so far?
Did you eat out prior to that?
Is he having vomiting and fever as well ?
Hospitalization is advised if he is not taking any fluids orally and is dehydrated with drop in blood pressure.
What I suggest is go to a ER physician and get the clinical examination done for temp, pulse , blood pressure , dehydration.
In case his vital parameters are fine he shall recover with oral medications like:
1. Oral antibiotics (Because its been 6 days) . Tab Ofloxacin - ornidazole course for 5 days.
2.Oral anti secretory agents (tab redotil ) short course for 3 to 4 days .
3. Oral Proton pump inhibitors - domperidone tablet like Pan D once daily before breakfast for about 7 days.
4. Oral rehydarting solution (ORS): Frequent sips as much as tolerated to prevent dehydration.
But at any point if he is not able to retain the oral medications and throws up , or oral medications are not helping and his dehydration and frequency of loose motion worsens then do take to hospital immediately.
He shall need IV drips and IV antibiotics.
Also in that case investigations suggested are: 1. Complete blood count
2. Stool for culture and sensitivity.
Thanks.

Hi welcome to Health care magic forum. It appears that he is having viral diarrhea. It usually take some time for cure in spite of treatment in the meanwhile patient must be infused with fluids, to compensate the loss of fluids. He is not lacking of salts means he must be having hypertension which compensates the loss of salts.
Besides i advise you some diet recomedations as take more of curd, bland foods like boiled vegetables, less oily biscuits till he get relief of symptoms.
Avoid taking spices, chillies, junk foods, oily foods, non vegetarian foods to avoid gastric irritation. Wishing for a quick recovery, and thanks for calling.