I'm Scared of Everything

I'm 13 and I'm afraid of everything, ghosts, the dark, and a whole bunch of other stuff. When I go in bathroom I can't look in the mirror, I'm scared I'll see something behind me. But I'm especially afraid of the dark. Sometimes I wonder if it's just all in my head but I feel like there really is something in the dark. When I tell my mom she just says:

"Don't be silly, stop making stuff up! "

But it's not silly to me, every time I hear lightning I feel like I'm going to die of fear.

My grandmother said that it's nothing, that there's no ghosts but that's not true. There are ghosts and I know there are. Whenever there's a ring at the door and I go to open it I always hear noises from the bathroom (something falling, crashing and all sorts of sounds). And every time I go inside to check there's never anything that's fallen over or anything else. What could this possibly be?

Please tell me what's going on, and not just the sort of "You're insane, go see a psychologist" and so on, give me some useful advice. What should I do and how should I stop my fears?