Is this a yeast infection?

Sorry for the grim picture. I had tests about 7 months ago and was told I had a yeast infection then. The doctor gave me successively stronger medication to treat a yeast infection but the problem never went away at all with any of these medications. I was tested again to make sure that it definitely was a yeast infection and I was told that I no longer show any signs of yeast. However I am still getting this discharge, that looks exactly the same as I was experiencing when I definitely did have a yeast infection. The only thing that seems to help is Canesten, but only temporarily. Every month a few days after my period I have this same thick white discharge, I take Canesten, the problem goes away and then a few days after my period it comes back again. There is a burning feeling if I sit with my legs crossed but that’s the only symptoms I really have. I have cut out scented toilet roll, tampons, pads, panty liners, I’m not sexually active, and in general nothing goes near my vagina except cotton underwear. I have been tested for diabetes, syphilis and gonorrhea and they have all came back clear. Is this a yeast infection or something else? It’s driving me insane!