Weight loss is a common symptom for untreated diabetes.
If you have high BG, your body cannot get the energy is needs from the food that you eat.
Therefore, it may breakdown your muscle and/or fat which results in weight loss.
Once your BG starts to stabilise at a lower value, your weight will start to level off ... and you may gain weight.
However, there may be other reasons for weight loss so if you are concerned it may be worth seeing a doctor.