I am experiencing toothache. i am the only person in my family that gets cavities and i brush and floss regularly! why does this happen?

Lots of reasons: Lots of things influence cavity formation besides oral hygiene, including, but not limited to, alcohol consumption, sugar/starch/acid dietary choices, eating disorders, genetically driven tooth anatomy, and so many other factors. Talk to your Dentist about fluoride supplements, sealants, and diet. Make sure you have regular 6-month check ups.