Well cozy, we have proven on this bulletin board over and over again that it is we, the posters who have it wrong. Sex is only supposed to happen at prescribed times when everything is perfect and is the first thing to be scrapped for issues both small and large and is without a doubt too superficial to even merit discussion most of the time.
That being said - what have you read on the subject, what counseling have you or she had, any affairs on either person's part, any physical issues with either of you etc...... More information might help.
The men on the board have said over and over again that No More Mr. Nice Guy and The Way of the Superior Man helped a lot. You will NOT get any more sex than you are having by placating your W. You won't get any sex by doing a bunch of things for her hoping for some. You won't get any sex by apologizing for who you are. What kind of guy are you? What do you like to do? Are you showing that guy? Are you doing the things you like to do?? Do you appreciate and compliment your W independent of trying to get some? Read some of hairdog and Lou's threads to get the idea.
Posts by Stigmata, Blackfoot, Burgbud, Corri are pretty helpful to see what is happening in a more dispassionate way. Don't overanalyze but learn to see your interactions with your W for what they are - part of a mating dance- a single misstep is ok, repeated missteps and well, the mating is over.