I'm sorry your mom isn't more supportive or understanding. I've gotten similar reactions from some family members when trying to talk about my own troubles. My personal opinion is that this type of response comes from fear, like they are afraid I might be trying to blame them for my troubles so they get defensive when I try to talk about it. Or maybe they feel guilty, as if there was something they could have done but didn't.

Otherwise, why would your mother dismiss your feelings? But again, this is just what I've observed in my own life.