I had thrush when we were TTC and was told the same as Buttersmum - canesten cream was fine but not to use it internally.
BUT (TMI) I have it at the moment and was given the 3-day treatment by the pharmacist and when I read through the info inside it actually recommends using it at the end of pregnancy?!

No warnings about not using it when pregnant at all (this is the tablets with the applicator).
I'd just go with what your pharmacist recommends hun