The reducing substance positive is suggestive of lactose intolerance
However don't go by one test.
Also there may be temporary intolerance after a bout of diarrhoea
There seems to be no infection now.
Continue breast feeds.
Gve some oral electrolytes available in sachets.
Redo stool examination after 2-3 weeks for reducing subatance when not on any medicines or oral rehydration solution.
Then furthercouse can be decided!
All the best