Hi, first of all please could you update your location as it will help us with products etc. You have been given Canesten by the sounds of it which is not that effective on Ringworm.
Have a read of this thread though
http://www.theguineapigforum.co.uk/threads/ringworm-hygiene-and-pictures.115402/
Ringworm needs to be treated systemically rather than topically so I would always recommend treatment with the oral medication Irtrafungol. Imaverol dips are also effective, and can be used at the same time if needed. Both are covered in the article.
Here is a link to buy the Imaverol dip in the UK without a prescription, please note it is a dip and should not be rinsed off.
http://www.hyperdrug.co.uk/Enilconazole-100mg_ml-100ml-Imaverol/productinfo/ENILCON/
I think your vet needs to take a sample to see if they can carry out a culture to show if it is Ringworm or not, though it does not always show up under a UV light. All other types of fungal rarely culture using the standard medium. The treatment I have recommended would also be effective for other types of fungal, such as Candidiasis.
For Itrafungol my vets use the cat treatment which is 1 week on 1 week off for 3 rounds, it carries on working on the weeks off so the treatment is effectively for 6 weeks. I know some other vets use it differently, but this was confirmed by the company that make it as being most effective.
The Imaverol standard treatment is dipping every 3 days, however, I have been advised to dip once a week otherwise you are not giving it a chance to work, this would be for 4 weeks in total. I also apply topically to the affected areas between dips. Please note that the whole pig needs to be dipped, and the Imaverol needs to be worked in using a throw away sponge or some members apply with a syringe.
You will find that there are different opinions on when to dip, and dosing etc, I am going by what was recommended to me by a friend who runs a Guinea Pig Health and Welfare clinic and has worked for numerous pigs there. However, see what your vet recommends.
If you are in the UK and need a more knowledgeable vet, please use our recommended vets locator.