Help my cat's Yeast Ear Infection came back!

About a month ago,  I noticed that my female cat was shaking her head like crazy.  I looked in her ear and it looked like it was really dirty.  I took her into the vet and she said that she had a yeast ear infection.  She then tried to tell me that there was a possibility that my cat has Feline Leukemia.   I don't know how she went from an ear infection to Feline Leukemia but it started to make me worry.  My cat was a stray when she was found at about 1 month old.  She did test positive for feline leukemia but was retested a few months later and was negative (I got her from a rescue who had all the testing done by vet). It was explained to me that there is a chance of a false positive test with small kittens.   If she had not been negative I never would have taken her into my house as I already had another cat.  She is now 6 years old.  I thought the vet was perhaps trying to get more money out of me by scaring me about the feline leukemia and wanted to test her again.

The vet gave me trasaderm to put in her ear.  It seemed to work as I took her back after 2 weeks and they said the ear was clear.  Well I have noticed that her ear is smelly (it was really stinky when they cleaned out ear).  I guess I need to take her back as it seems the infection is not gone.   But this has me thinking that there is a possibility of she could have feline leukemia.   Should I be worried?

I went through repeated yeast infections in my cat's ear many years ago.  The only thing that cleared it up, finally, was BNT ear ointment.  http://www.bcpvetpharm.com/news_bcpbnt.html   It's a goopy gel medication that the vet injects in the ear and it stays in for about 2 weeks for the cat's body to absorb it all.