your pancreas is still producing insulin, maybe this is reducing so your insulin requirements may be rising, this could be why your blood sugar is rising.
Have you been given any information about adjusting your insulin? If not, if you are worried you could give NHS Direct a ring - 0845 46 47 - they might be able to help.
Don't worry though - a short period of increased blood sugar (with no ketones) won't kill you. On Monday, you need to contact your diabetes team and tell them about the increased blood sugar, they might want to adjust your insulin.