Why do I cry over stupid stuff and not like stuff that would make most people cry ?

I cry over not being able to do something, being embarrassed and not knowing the answer if a teacher wants me to answer. But, I didn't cry that much when My grandma died, a few tears fell and I was super sad but I didn't cry as much as I do over stupid reasons, I actually felt bad... I don't like showing my emotions but whenever I get embarrassed I just burst out crying and then I feel so dumb because i'm crying over nothing. Is anyone else like this? Do you have any idea why I don't cry that much over serious things?