focused.on.health
the burning sensation in your stomach is probably the elimination of a mixture of stomach acids (weakened) and bile, where the body will use any avenue it can for elimination: hence the nausea and the possibility of vomiting or even diarrhea.
The sweet taste in the mouth is normally a sign that the elimination process has finished (which is highly unlikely after day 6). Dr Tilden reported that after an extended fast the secretions are normalized resulting in (amongst other things) that the fast is nearing its conclusion.
However, I wouldn't come to any hasty decisions as to why, as this symptom could easily change within the next few days to a week or so.