Coughing is the body's way of getting rid of an irritant, be it viral, bacterial or an allergy to any substance like dust, dust mites, feathers, smells and so on.
As this is a dry cough, and being a diabetic you should not be consuming sugar laden cough syrups, get up and have a warm drink.
You can now buy throat lozenges that contain no sugar, so you can try those to help soothe the throat.
If it does persist for another week or two or you get worse, make an appointment to see your doctor to check your throat, as you may have pharyngitis. But do drink plenty.
If you are OK with a teaspoonful of honey (as part of your food allowance) that that with juice from a fresh lemon in hot water is very soothing for the throat.
You could try and take some Melatonin, it's a natural sleep aid. Also if you have not done so already, try and sleep propped up like you are in a recliner.