Our body has a biological clock that works and functions in a rhythemic pattern. A change in it can disturb our normal functions and cause sleeplessness.  Its completely a adaptive procedure. In your case your shifts keep changing too frequently with a span of only a week.  This makes difficult for our body to accustom to the changed needs. Try changing you shift pattern to long schedules if possible. Have enough nutritious food with more fruits,  nuts etc.  Dont get used to more stimulants like coffee,  alcohol etc. Avoid eating fatty and oily foods. Have adequate water intake.  Try to take short naps in between work period if you need and feel unrefreshed.