To be honest, I wouldn't go with anything less than the 7 day treatment for a yeast infection, regardless of the brand. My doctor told me NEVER the 3 or 1 day treatments because there is such a concentration of medicine in it, that if it is not administered perfectly, it worsens the yeast infection.
At this point...I would go to the doc to clear it up. They'll give you the happy pill, and you'll be happy.
Did you use a condom with any sort of lubrication? Sometimes, women have to get used to the condom. Are you allergic to latex or anything? Also, did you urinate after you were done having sex? Many women get infections from sex (yeast and bladder), and urinating helps prevent these infections.
I wouldn't worry about the sex causing the yeast infection. Just get it cleared up by the doc, and don't have sex (or do anythign sexual, really) until it's all cleared up!