I need to count the number of items in a column if some conditions are met in
other columns:

Col1 Col2 Col3
Item1 Yes Sep
Item1 No Aug
Item1 Yes Sep
Item1 N/A Sep
Item2 No Aug
Item3 Yes Nov
....
For this spreadsheet I need to calculate how many "Yes" for the items from
the first column for Sep, e.g..

I'm trying to use the array formular:
{=COUNTA($A$4:$A$1000=A2)*($C$4:$C$1000="Sep")*($B $4:$B$1000="Yes")}
But,it's not working.

Could anybody advise anything?

Thanks