Noted your detailed history and understood your concerns.
First of all since your HIV test is negative, nothing much t worry about unless the repeat test after three months are positive. Also needed is to get the STD panel done to rule out other venereal diseases.
Your concerns is about gastritis
and oral changes as you have mentioned.
I would advise you the following in such a situation:Consult a Gastroenterologist
to get an upper GI Endoscopy and other relevant investigations to see for the cause of gastritis.
Add Antacids to be taken when on empty stomach.Domperidone
for regulating GI motility.
As for oral lesions get stool tests as colitis and such condition can cause stomatitis
Add on Multivitamins and minerals.
Get Vitamin D tested and if less get supplements.Oral hygiene
Stop milk, milk products including tea as these give white coating to the tongue.
Pune has good medical facilities and hence consult your Family Physician for referring a referral to a proper consultant/ Specialist.
Hope I have answered your query. Let me know if I can assist you further.
Dr. T Chandrakant,
General & ENT Surgeon