Why are my emotions so messed up?

I think I cry too much and am too sensitive for a 15 year old girl. For example, tonight I started balling over something little. Me and a friend are going to the city fair this week and we hadn't decided what time we wanted to go. Everyone involved said it didn't really matter. For some reason, I felt like it was my choice to decide even though it wasn't. When I asked my mom, she got annoyed and I started balling like almost suffocating myself. After going to my room and calming down, I felt the need to apologize and did which led to more crying. I've also almost gotten out if a moving car while crying over something stupid. I don't understand why this happens to me. Is it normal? Thanks.