Sleep is intimately related to our mood and underlying medical illness and our other activities/sleep schedule. As you are working at night and with your shifts changing often, your sleep is disturbed to a greater extent. Once you start working night shifts, it takes almost 10-12 days for your sleep cycle to get adjusted to the new shift. If you are changing your night shift times often this will never happen and as a result your sleep would be disturbed.
Sleep disturbance can in turn affect your underlying medical disorders - it can lead to hypertension and metabolic disorders such as diabetes. In addition, it can lead to depression, anxiety, irritability, difficulty concentrating, etc. Since you have diabetes your diabetes can worsen. So you might want to closely monitor your diabetes/sugars as complications from diabetes can kill you. It is possible that your tiredness and thirsty feeling are a result of poorly controlled diabetes.
In any case, I would strongly recommend sticking to one particular shift for work rather than changing your sleep/work schedule frequently. And if you do night shifts, make sure that you have a specific daytime period (at least 8 hours) for you to sleep and during this time make sure that you are not being disturbed by external noise/telephone/others in the house, etc.