Why so sensitive?

I want to be tough. Not physically so but emotionally. I don't want to tear up everytime something gets me down. At this particular point, I think it's hormonal b/c it's been bad the past few days. Minus the hormones, I still have a problem with it. I don't know how or why this happened b/c this didn't start until I got way older. There is a such a thing as too much sensitivity. Not saying that I'm overly sensitive but somethings just shouldn't bother me.