How to stop being shy!?

I have really bad trouble with shyness and i just generally have no self confidence. I am constantly having panic attacks before and during anything social such as school or parties and I have ended up basically staying in all of the time because I can't stand the feeling. When i am around people I am always in my head asking why they would even want to speak to me and I am certain I am boring them and they want to speak to somebody else. I think it stemmed from a break up I had, I just lost all my confidence. Since then I have avoided any awkward moments or anything that is out of my comfort zone that i might get embarrassed by. I did at one point think it may be social anxiety disorder and took a few tests that came out as positive on the internet- but then you can never trust if they are legitimate. I have tried quite a few things such as yoga and meditation which I have heard have helped others but I just can't seem to budge the feeling and i am worried that, now I am about to go on to another school, I won't have the confidence to make any new friends and end up alone and even worse. If somebody could help me or they have some advice from their experiences with this it would be really great! Thanks