Sensitivity

I'm not quite sure if we are born with how sensitive we are going to be or if we gain this by experiences?  Lately I have realized just how sensitive I have become in the last year to year and a half. Is it because of a certain event, or is it something that I was born with? The people I love the most are the ones that I seem to be the most sensitive about too. Do I really need to get so upset at the little things? I know there are certain things that I should be sensitive about, but not the stuff the am. I'm putting this on my list of things to work on, I'm starting my summer resolutions, no more stress from school, and no more hyper-sensitivity.