you shouldn't be so worried about it. Most likely, this is a psychological disorder. You feel nervous in some situations, which leads to the body reacting differently (in your case, blushing). After you have become aware of this blushing, you get nervous about getting nervous.
For example, say you are at the mall and you bump into a group of people that you know. Because you are afraid of blushing, the first thing your body is going to do is become nervous. You say to yourself, "Oh no, I'm going to start blushing". Or something like that. Then of course, because your nervous about getting nervous, you begin to blush.
That is probably confusing, but for an answer...try meditating or some soothing exercises. Don't try medication right away, I'm sure you can fix this yourself. You just have to learn to stay calm in certain situations, and not worry. Eventually it will go away if you learn to not stress over it.