I second going to a school counselor. My dad is like your mom, unable to acknowledge pain in others unless it's "bad enough" according to his criteria. And if he thinks he's felt anything similar to it, then it isn't bad enough. However, this is just plain old denial. Just because your mom doesn't believe it's bad, doesn't mean you don't have a problem. You deserve help for it.
I also agree about not masking your feelings, hiding them, etc -- I've done that my entire life and it has caused major problems for me that I'm still dealing with now in my late 30s. Reach out to your school counselor, hopefully they'll have some ideas about how to get help even if your mom isn't on board!