The problem you are facing is only in your thoughts. Believe in yourself that you can perform well before public.Have self confidence. Always think positive. Do meditation
. This will help you in overcoming your problem. There are medicines also which will help in maintaining calm of your mind. But take them only under medical supervision. But my advice will be that focuss on meditaion and yoga. They will really benefit you.
I hope this is of help to you.