Working off shifts up to 12 hours, trying to get minimum of 6 hours sleep, but i am tired every day, took some time of but i have trouble concentrating, decided to quit caffeine and eating better but need advice what i can do to function while awak?

Several options: Definitely keep getting at least 6 hours of sleep , & short periods of exercise (20 min walk) can energize. A little caffeine is quite safe. Protein with meals & smaller more frequent meals tends to energize more than large infrequent meals; some carbs are needed for immediate energy. If long term issue with fatigue you may need to see a Dr & have some basic lab work (blood count/sugar/thyroid)