Hi Nick,
Infections, stress and other factors can and do play havoc with diabetes control. It is important that you keep a eye on your readings, write them down and also record all your food intake (carbs) and insulin doses to see if there is a pattern developing. As you know, in time our insulin requirements can change, so it may be that you may need increase/decrease your insulin at certain times of the day to combat the highs and lows. Keep trying to get in touch with your DSN, I am sure they will look at your results and offer some practical advice.
Best wishes
Nigel