What could I do?

There is nothing wrong with what you are feeling as it is quite normal. You are young and striking out into the world. I want to congratulate you on your graduation, that is a great accomplishment and chance for you to do well in life. You have plenty of time to socialize and become comfortable with interacting with others. I see you are new here. Use this site as a social tool. You can get some practice conversing to different people. Most of all here you have to help yourself I think. You have to find whatever it is that will break you out of your shell and shake the fear your have. I used to be kind of a shy guy myself. I still made friends and as I got older I got more comfortable with who I was and that made me less fearful of the interaction with others. You have the whole world ahead of you! Relax and enjoy it.