Several things to consider.
Have any of the ingredients you use changed? Have you changed brands?
Some times when one makes a certain recipe often they don't really measure correctly - could that be part or all of your problem?
..........a great tip, which might help with the "oil" factor, substitute apple sauce for equal amounts of vegetable oil that you use in your cake recipes. Its healthier, creates a very moist cake, and the flavor is the same, without the "oil"...