We can say "you have got butterflies in your stomach". 1. We use this expression when somebody is nervous before a public speech or a theatre performance. 2. We also use this expression to describe the feeling of being in the company of somebody you are attracted to. For example, if you like a man and you are in his company and he leans in close to you, you might get "butterflies in your stomach". You also might get butterflies in your stomach if he looks you in the eyes. http://blogs.discovermagazine.com/crux/2017/02/21/butterflies-in-the-stomach-science/

It seems you're looking to describe two different feelings, and there are many ways to describe each. You could also use any number of physical reactions that happen when you are nervous or excited - "My heart raced". "My hands were shaking". "My palms were sweaty, knees weak, arms heavy" "My adrenaline surged" or the more extreme "I pooped myself", but that usually means fear, not nervousness. Similes - "I felt like a kid on Christmas" Metaphors - "I was a kid on Christmas" Other similar feelings could work as well - "I was in love (with whatever was making you excited)." "I soared through the sky" "I felt trapped." "I froze."