So I went to my dentist today, I'm 14 years old and she said I have the smallest hint of a cavity coming, how can I stop it getting bigger? She put some fluoride varnish on my teeth.. this is the first time I've had anything ever happen to my teeth.. I brush two times a day with Sensodyne gentle whitening toothpaste and rinse with Listerine Total Care. She told me to cut down sugary foods, but I've just got such a sweet tooth! I drink a lot of fruit juice also, and I know that its high in sugars and acids, how can I substitute it?

How can I stop it getting bigger?
How long until I can eat/drink after having the fuouride toothpaste being put on?
Am I supposed to brush my teeth the same night I got the varnish put on?

Thank you!