I am a nutritionist and Kinesiologist, and I work with university hockey players, responsible for all of their dryland training, diets, and strength training. A lack of endurance should not come from working swing shifts, as long as you are getting good REM sleep. I would say that your diet is out of whack, you are probably eating meals at night a lot, instead of eating healthy, low carb snacks, and eating meals at the normal times. (Breakfast when you get home after nights, lunch when you get up, then a snack and dinner before you go in to work. You should easily be able to get through the night with healthy snacks like Jerky, nuts, and other healthy alternatives.
If you are out of energy by the 7th hole, its certainly a fitness and nutrition problem. That, or a serious, undiagnosed medical condition. If you truly do all the things you say, I would be getting a very good checkup. There is nothing normal about what you are describing. Nine holes should be a warm-up for a young man of thirty.