Why do I start crying suddenly?

I can't stop crying, I have no one to talk to, if I talk to my mom she'll ignore me and think it's stupid that I'm crying for no reason, and I can't trust my friends with secrets, they tell everyone, but I can't stop crying, and I haven't been doing anything that makes me cry (cutting onions, etc.). I don't know what to do, no one can help me, and if I appear like this in front of my family they'll start saying that I'm being stupid or such.