How to Cure Fleas in Dogs

my question is regarding fleas not mange. I bought the Frontline in a pet shop to use once a month on my dog but she still scratches and she I can see some blood somethings on her bed. I also bought the frontline spray to put on her but she has a lot of fleas. DOES VInegar works to kill fleas I am scared that I am going to poison her with so much frontline. thanks a lot.