Yes, it is normal for higher readings when you are ill. Keep testing regularly and make sure you keep a diary of how the illness progresses and what readings you took - it helps massively to build up a pattern so you can refer back to it 'next time'.
If you have a reference point, it will greatly increase your confidence in managing the condition, rather than have it control you.
I have always kept a diary of all testing since diagnosis, and believe me it's a great reference tool as it's surprising how much you do forget. 10 seconds of your time to write it down, pays dividends in the future.