It is interesting to observe that diabetics as such does not cause tiredness, it is more the symptoms that cause it. Diabetes is more an imbalance of blood sugar levels that creates an imbalance in energy. Continuously monitoring glucose levels makes diabetics experience constant dips of blood sugar that makes for severe draining of energy and tiredness. So diabetics are drained of energy even for doing simple tasks.
Eating improper meals or skipping it could also cause tiredness. Taking a wrong dosage of the diabetic medications or not following it up with food could cause tiredness. In case you are not able to combat tiredness with effective diabetic control measures, do consult a doctor.