How can I be more confident?

Well you can try some simple techniques. You can stop for a minute when you are in these situations and just think about a time that made you feel really comfortable and take a deep breath and take it all in and remember that you are capable of being free from others thoughts. For example can you remember playing as a child and how you would smile and had no worries about what the other kids thought. Well like acting you can put yourself in that very mode with large crowds of people. Remember to give love to your inner child and your confidence will boost. Hope this helps any.