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As said in your query that your throat swab report is indicating only heavy flora, and no other pathological bacteria is isolated but still you have burning behind the throat and at the same time you have an ulcer on tongue.
Your all these symptoms are favoring aphthus ulcer along with GERD
( gastro esophageal reflux disease
). There is another possibility of oral candidiasis
To diagnose it properly and for treatment point of view you should do-
1- Culture for fungus in throat swab.
2- Examine the teeth adjacent to ulcer for sharp edge.
3- Upper G.I. endoscopy
to rule out gastritis
by above investigation and there co-relation with examination finding one may reach to correct diagnosis, that may be accordingly plan for treatment.