Hi emzie.
Welcome to the boards ... not that I'm a very outspoken character myself. (I've hardly posted, but I do read.)
My endocrinologist (a specialist in treating diabetes) states that if your blood sugar level is over 14 mmol/l (that's 252 mg/dL if we have any American cousins reading) you should check for ketones.
Ketones, as you may already be aware, come about due to the improper breakdown of fat and muscle tissues as a result of continuing high blood sugar levels. (It's your body's natural defence mechanism in an attempt to survive. When your blood sugar levels are consistently high it's indicating that either you don't have enough insulin present (type 1) or your body is resistant to the effects of the insulin (type 2). It therefore can't use the glucose (the simple sugar that you test for when you do a blood test) that's present for making energy and keeping you alive. It does the next best thing that it can, and that is break down fat and muscle.)
I'm not sure which type of blood glucose meter you use, but some of them can use test strips to check your ketone levels. (I use the Abbott Optium Xceed meter, which can do this. This gives a precise reading, rather than that that you get with urine testing strips.)
One thing you could do is ask someone close to you if they can smell anything on your breath. When you produce ketones it tends to make your breath smell like acetone (one of the ketone bodies that are present) ... you might know it as nail polish remover. ;-)
Having ketones present is, as I'm sure you're already aware, not good for you. Ketones become present when your body reaches a state of ketosis which, if not brought back under control, can turn to ketoacidosis ... where you blood becomes acidic and so, more damaging to your body's organs. This can often result in you needing to be hospitalised ... until such time as your blood sugar levels are back under control. Obviously, you want to avoid this situation.
I agree with LittleSue that the symptoms that you mention could quite easily be other things happening, so you mustn't use those as an indication that you have ketones present.
As LittleSue states, if you don't know how, or are not confident in adjusting your insulin doses, do please seek a medical opinion. (If you can't get in to see your GP, telephone your local hospital and ask to speak to someone that deals with diabetes. If it's 'out of hours', speak to someone in A&E, mentioning that you wish to speak to one of the diabetes team.)
Best of luck for now and for the future, emzie.
Lots of Love and Light.
Mick
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P.S. Please don't be offended, or alarmed, at the "x's". It's merely a logo, of sorts, that I've used for some 30-odd years now.
P.P.S. If you're in the UK and you are prescribed medication to treat your diabetes ... either pills or insulin ... you don't have to pay for your prescriptions. Speak to your doctor's surgery to start the process of getting an exemption certificate.