HI WELCOME TO HCM
i had gone through your query and understand your concerns. i would come up with two possibilities.
1.the first one may be,PEPTIC ULCER
may be the cause;upper gastro intestinal endoscopy
may confirm the diagnosis
2.second possibility for oral cavity is,GINGIVITIS; gastro intestinal diseases,is poor oral hygiene
are the predisposing factors
I hope this is helpful for you, thank you