Smit, while your consultant may mean well I am sure you and I can't be the only one's whose bodies arew reacting in this way! Not a good thing to tell a patient in my opinion. Hmmm.
I have also had high-ish readings, say 13mmol, and have had extra insulin, eg four units of Humalog, and an hour later it's still not gone down much. It is very frustrating as I, like yourself, I don't want to set myself up for a big crash in the night. It also seems more unpredictable in the evenings too, have you had this...?
Just keep testing, injecting if you need to and snacking if you need to too. Rubbish, especially if you are like me and normally are very much on top of things, I know but hopefully things will settle down a bit (or you'll get used to the different doses and reactions from your body.)