I have to go with luckyR on this one.
IF, IF, if, you are truely a good doubles player, then that means ou have all the shots and are supremely aware of player positions and cour tactics. That is a good thing.
Compared to doubles, singles should be a simple and straightforward game.
Having said that, it may be that you are lacking some of the skills that are helpful to the singles game. Only you can know what they might be.
Doubles is a game of serve/volleys/chips/sharp angles/quick and decisive points.
Singles requires somewhat different qualities that you may need to master before becoming a dominant player. You need to have deep. consistant groundstrokes, patience, the ability to change your pace/spin and set up your shot. The first serve is also more important in singles than doubles for winning easy(ier) points.
Without going over all the differences, I suggest that you review in your own mind your singles strenghts and weaknesses, and determine what skills you may need to beef-up for your singles game.
Good luck,
B