I am really shy, why? and what should i do?

I would change the way you think, instead of freezing just say Hello or smile and take it from there I beat nothing bad or scarey happens to you. Its good you obviously want to change which is a good thing and at the end of the day we all have to be on our own in life even right through into adulthood there are times when we are on her own. As humans we feel better with company and someone around us but its not always possible evey minute of life. So you are dealing with it now which is good in away there is nothing to be scared or and being comfortable with your self will come with time. Try a different approach and see what happens start with a little and build on so people dont think you hate social interaction and then it will get easier and easier. You may even find you have more friends too. Then in the future you will be better prepared for work and even holidays etc Good Luck start small