I brush more than four times a day and use flouride, but i still get cavities, and my teeth are white. what can i do?

Diet and flossing: Are you flossing? That will clean the areas between your teeth where the toothbrush doesn't reach. And what about the foods you eat... Are they sugary? Lots of sodas & candy? If so, re-evaluate your diet, since many of these foods will cause cavities to form no matter how much you brush and floss.

Additional thoughts: Dr davantzis gave you an excellent answer and i agree with him. I would just like to add a few comments. First, you may be brushing but not properly. Secondly are you brushing (and flossing) after and not before eating (including snacks). Finally, your own dentist is the best one to evaluate and recommend changes in order to reduce the number of cavities you get.

Re-evaluate: First, it's not how many times you brush, but how well. Also, you never mentioned flossing. If you don't floss, decay will occur between teeth, by the contacts. Also, how often do you get professional cleanings? And don't forget Fluoride in toothpaste, applied by your hygienist, and possibly in mouthwash!

Multiple factors: Tooth decay is caused by acid from bacteria and/or foods dissolving away the tooth structure. In addition to tooth brushing and Fluoride use you need to evaluate what foods you eat. Are they high in acid? Some medications or medical conditions can cause dry mouth and lessen you salvias ability to neutralize acid. This may also be a factor. A good dentist should be able to give you more guidance.

Look: Look into adding xylitol to your routine. Although Fluoride and brushing are great in reducing cavities, if you have other factors such as reflux, acidic saliva, dry mouth etc...You can still get cavities. Xylitol appears to be effective in countering some of these things.