Thanks for your query, I have gone through your query.
The possible causes for the burning sensation in the mouth could be because of lichenoiid reaction that is
allergic reaction to the tooth paste or it can be because of angular chelitis secondary to
anemia or it can be a aphthous ulcer.
Consult a oral physician and get yourself examined to rule out these things.
If it is a lichenoid reaction then you can change the tooth paste and use
topical steroid like
triamcinolone acetonide 0.1% 4-5times daily after food.
If it is because of angular chelitis improve your nutritional status, consume lot of leafy vegetables.
If it is aphtous ulcers then, you can take topical
anesthetic and analgesics like anabel gel. apply 3-4 times daily before food and topical steroid like triamcinolone acetonide 0.1% 4-5times daily after food.
I hope my answer will help you, take care.