Oh you poor thing. I was the same when I was pregnant with dd (also my third) I had recurrent thrush almost all the way through the pregnancy.
Have you tried taking pre and probiotics? They can help to rebalance your system and encourage the good rather than bad bacteria. You can get them from good health shops and they decent ones should be kept refrigerated.
Another good thing to do is drastically reduce your sugar intake. Not only refined sugar but things like refined carbs (white pasta, white bread etc), dried fruit, bananas etc. If you have a lot of sugar in your system it helps the yeast to thrive by changing your ph/bacterial balance.
In terms of comfort, if the cream isn't helping, try dropping a couple of drops of tea tree and lavender oil in some boiled cooled water and soaking either some cotton wool pads or flannels in them. Apply directly to the affected area several times a day, particularly after using the toilet. I found this really helped to relieve the 'heat' and discomfort. (You need to boil wash the flannels after each use though.)
I read that the yeast organisms in thrush have started developing a resistance to clomitrazole (the active ingredient in Canestan) there are different treatments available but GPs are reluctant to prescribe them as they haven't been tested during pregnancy (neither has Canestan, but it has been used enough for them to say they 'believe' it to be safe unless taken orally).
I have also read that there are homeopathic treatments available, but only if you visit a qualified practitioner.
You have my sympathy, its hard enough being pregnant without having that to deal with as well. Hope it settles down for you soon.