I do believe that one of the issue with Southwest Airlines lately is the price of oil...now before you tell me that oil is going down, read below.
Several years ago (as in at least 5), when oil was headed up quickly, Southwest brokered a deal whereby they purchased large amounts of fuel tied to a $40 per barrel oil price, so when oil shot up to $70, $80, $90 per barrel, Southwest was able to price their flights way below their competition. It seems that lately, those contracts have all expired and Southwest has had to find other ways to keep their costs down, e.g. cutting flights.
Anyway, this is all from memory, so the details may not be exact, but the facts are basically correct.
Enjoy your trip!