Overcome my shyness and blushing?!

OK so growing up I was the kid that liked to have fun and get along with everyone, I usually thought of other more than myself. I was doing alright for the most part, if a girl talked to me, or a teacher gave me hard time to embarrass me in front of everyone I would be OK I didn't turn red or blush and I know how to combatant with things for the most. As I entered middle school i noticed things started to happen to me, such as becoming awkwardly shy in front of girls, or even getting embarrassed when a teacher cracked a friendly joke here or their. This progressed all in middle school I would rarely talk except only to my friends which I felt comfortable with. When a girl tried to talk to me I look back and feel bad for shunning them away completely because thinking about it I always felt like a total hideous loser for being the short overweight kid in school, that would be the subject of getting piked on from time to time. Getting picked on rarely bothered me it just seemed OK to me no harm done as so I thought. So basically you can say middle school were not my best years. Now it was coming to be time for high school to start, but I began to notice differences in myself (puberty). I grew taller and I wasn't as overweight just average for once. People were surprised as to how I changed over the summer. I still felt the same, as if i was in middle school though. As time went on i met new people and some girls but i just saw them as friends. Their was this girl that I would see time to time that I kind of had a crush on though but never relay got the courage to go talk to her. But one day she had noticed me and said hello, and I had blushed, i hate myself everyday for that moment I didn't know why my face got red It just did and she did a lil giggle and walked away I was so embarrassed. More time went on and my appearance changed even more, I was beginning to get more remarks from girls on how cut and handsome I was. This didn't really make me blush anymore just kind of tense up a bit. Now it is my third year of high school and not to sound like one of those vain people but people say Im not that bad looking of a guy(where as I believe I am a very hideous looking guy), and I am probably the most awkward socially shy person their is. Ill be in a group discussion with people I barley know and I wont say a word because my shyness get the better of me. I still see myself as the middle school kid. If a teacher were to pick me for answer and if to much people were to look at me I would get a tense feel of pressure and choke up a bit and probably get red of shyness, my presentation grade have suffered from this, where I feel very nervousness to be chosen to go up in front of a class and talk. I just wish for help and advice on how to overcome my self from being to shy and get rid of my red blush.