The smell from the septic tank, and the mold can both cause the symptoms of diarrhea and vomiting that you are describing, especially if the symptoms are causally related, meaning that they are worse when you go in the vicinity of the 'mess'.
Only further testing and avoiding the environment (i know it is easier said than done) will help resolve the symptoms.
The treatment would be depending on the reports, but ensure that you take a light diet with plenty of fluids, preferably in small quantities frequently (to prevent nausea)
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Dr. Gupta