Brief Answer:
Herpes infection, pemphigus, topical steroids, bacterial infection

Detailed Answer:
Thanks for your query. I have gone through your query.
As far as the blisters in the mouth is concerned, I have two possibilities.
It can be secondary to herpes virus infection leading to herpetic gingivostomatitis. The other possible cause can be because of pemphigus or bullous pemphigoid.
Nothing to be panic, consult a oral physician and get it evaluated. Mean while you can take a course of topical steroids like triamcinolone acetonide. For the pain you can take topical analgesics like choline salicylate. Do saline gargling.
Regarding your stomach upset, it can be because of bacterial infection or gastritis. You need to consult a gastroenterologist and get it evaluated. The drugs you are taking food can be an antacid for gastritis. Go for a colonoscopy and get the dignosis confirmed.
These are the possible diagnosis and treatment plan based on the description of your problem provided by you. If you can upload the images of the blisters or the lesion, I can give you exact diagnosis and treatment plan. Please do follow up so that I can assist you better.
I hope I have answered your query. If any queries are there reply me back. Take care.

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