Hi,
Could be many reasons. Lots of things to consider.
Have you checked that your Lantus is OK? - i.e. Not out of date? Not cloudy? That it has been stored properly and not got too hot? That you are using a new needle at each injection? Do you need to up your Lantus by a unit or two? Do you think you are fighting an infection? Can you check for ketones? If ketones are high seek medical advice immediately -
link to info on ketones. If your high sugar levels persist please seek medical advice.