Its called ketoacidosis, you should talk to a doctor about it. My mother was a nurse and worked in several parts of the hospital, and if I recall correctly it happens if you forget to take your insulin or have too much sugar in your blood.
I'm another volunteer here, also not a physician. BL offers good advice and I'd like to offer an additional suggestion.
Visit your dentist for a complete checkup of your teeth & gums. Bad breath is often an indication of underlying gum disease -- which, if treated early, can be managed with very careful home care including brushing, flossing, mouthwash & using some special instruments to disrupt the bacteria enjoying the "sweet life" under our gums. Untreated, gum disease begins to erode the bone that holds our teeth. SUrgery can correct that if it's not too advanced, and again -- rigorous home care is needed.
Dentists & periodontists often are the first to diagnose diabetes because of the damage the high blood sugars have one. Talk to your doctor & get a visit to your dentist soon, too.
Dear Sally,
I have never heard of any form of insulin causing bad breath but i can see how it may because food is only partially digesting. Thirty years ago when i was diagnosed with diabetes my now ex-wife told me my breath was bad and so i was brushing and rinsing after every meal. Unfortunately i don't know much about low carb diets but they can strain the kidneys which may also help contribute. It may be something a doctor can resolve.
Good luck, bret