I used Canesten also while I was pregnant.
During pregnancy a pharmacist will generally ask you if you have had it diagnosed previously.
As i hadn't I had to go to the doctor, get an unnecessary script just to prove that all was ok.
If you have had it before and you're certain it's thrush it shouldn't be a big deal.

There is a high recommendation for using natural products like InLiven or Inner Health Plus as well. But i don't know much about them, just have them in mind for next time.