It's Body Dismorphic Disorder. Basically, a combination of a lack of certain chemicals, past experiences, etc cause you to literally not see yourself the same as others see you. People with BDD often become obsessed with particular traits and do a lot to try to hide the perceived flaw. You should look it up, and if you think you meet a lot of the symptoms, definitely go to a psychologist and ask about it. As it is, i think you should see someone to make sure you don't have anything at all.