This sounds awfully familiar to what I have been through. Please go to Wikipedia (or a library) and search for Body Dysmorphic Disorder.
To tell you a little of my history, basically I started feeling so ugly and deformed that I really thought I had to be the most hideous thing on this Earth. Like an experiment conducted by aliens to create a lifeform that resembled a human, but failed miserably. The feeling was so bad it made me unable to leave the house to go to the local store cause I felt everybody was disgusted by me. I have never been called ugly, in fact the opposite was for more likely to happen, but I didn't believe them cause in the mirror I could see what I looked like. Now I know the mirror lied.
You say you are in school, so I assume you are still a teenager or in your early 20's. In that age, almost everyone starts to feel uncomfortable with the way they look. However, with some people the worry will get so bad that they are suffering from it. It seems to be the case with you.
Please try to get help with this. You can start with talking to a school counselor, a general practitioner, or friends / family. I used to keep it to myself, and if you don't share it your worries will just pile up. I ended up in 20-hour a week therapy for 9 months, on meds, the whole deal. I was forced to quit my medicine study, couldn't go out, and at some point was unable to show myself to anyone but my parents, brother, and sister.
One more thing I like to add. The most important thing in how you look isn't exactly what you look like. You can have pretty hair, a good body, etc., but what matters is how you feel on the inside. Happy, caring people tend to be way more attractive than aggressive or grumpy folks. I guess this has to do with a certain precaution you take when you are talking to someone who is grumpy or very self conscious, cause you don't know what reaction your words will evoke.
Anyway, I think you just took a major first step in telling us here! Take care, and all the very best!