With my understanding of requierment , this is what need to be done.
Your load script should be as below.
LOAD * INLINE
for i=0 to fieldvaluecount('OraField')
$(vFieldname) as Sales,
$(vMonth) as Month
This should group all the sales fields into single field.
Next step in the chart , you can use the previous function to show the previous month sales
Let me know if it helps.