I think that I am really really stupid. Could this explain why I am so obsessed with my looks?

Okay... my family tells me that i am brilliant but do not "try hard". The only reason why i got good grades in the past is b/c my parents basically did my hw for me and wrote my essays. I do not try as hard as I "could" b/c i am stupid which makes me not motivated. I like chemistry, biology, psychology, and creative writing (the ONE thing I am good at) and thats about it. Truthfully, i hate schoolwork and learning for the most part. In math cl, I would stay for extra help 2-3 times a week AND have a tutor, and still get D's and F's on the tests. I was in REGULAR math, but now I am in no math, and senior year (next year) i am taking a very basic review math course. My family is OBSESSED with education, and tells me i should focus on my brains. But how the hell could i focus on my BRAINS if i am soo dumb? I am now "clified" at school and take a study skills cl (this is very beneficial). My peers tell me that i am stupid but REALLY funny. For w.e. reason, adults think that i am the bright, studious type. The past year, i went from dork to diva, and am quite obsessed with my looks. I always try to be y with my clothes, and it IS my genuine style. I always look EVERY reflective surface that i see (even windows and car doors). But there is a problem, if i do not look good (liek if my zits arent covered, if my hair looks sh***ty, if i am bloated, if my pants look baggy) i feel inferior to other girls, and feel terrible about myself. When i am wearing a little makeup/lip gloss, showing off my 32D , and wearing juicy couture, i feel very arrogant (and genuinely feel gorgeous). What is this about? Does this have to do with being a moron?