How come I get a nervous feeling over stupid things?

Whenever I think of certain things I get nervous, even if I shouldn’t be getting nervous. For example, I recently went to Disneyland and got a picture with Peter Pan. I’ve loved him since I was a child, so I put the picture as my new home screen background. But every time I look at it I get really nervous and get a butterfly feeling in my stomach to the point I almost can’t look at it. This feeling happens with lots of things. Another example: I’m a theatre kid so I audition for things. If I think about an upcoming audition, sometimes I get the same feeling. Or if I think about a dance or vocal class I have to go to later in the day I’ll get that feeling too. Sometimes I even get the feeling when I’m about to do something as simple as text someone back! Why do I get this feeling??