Hi Katie,

That's quite a deep question & topic.
I would say that some people could be just "wired" that way - to be more sensitive.
There could be much deeper reasons behind it too.
Maybe even things that happened when you were too young to remember it. I'm not even meaning horrible things - maybe just an uncertain environment.

Also physical or health issues - like possible hormonal imbalances ?
Possible even some food sensitives or allergies might have some influence.