inserting multiple values into SQL with %
The % operator takes a string on its left side, and a list of values on its right side:

execute("SELECT ... WHERE B_MONTH = '%s' AND B_DAY = '%s'" % (currentMonth, currentDay))


Please note that using % introduces the risk of SQL injections when used with strings, so you should always use SQL parameters instead:

execute("SELECT ... WHERE B_MONTH = ? AND B_DAY = ?", (currentMonth, currentDay))