If you seem to get a lot of cavities, then you almost certainly have a sugar habit. By that I mean that you tend to expose your teeth to something sweet numerous times throughout the day. The key tends to be the frequency of exposure. Thus, if you buy one can of (sugared) soda (or even natural fruit juice) and then sip it throughout the day, taking a sip, putting it down and doing a bit of work, then picking it up for another sip twenty minutes later, each sip allows the sugar to coat your teeth. 
The  bacteria in your mouth metabolize some of it leaving a coating of acid on the teeth. This acid remains active for about twenty minutes at which time you take another sip starting the whole thing again. One bottle, or can may last a whole day, but that can contains enough sugar to cause huge damage to your teeth.