I don't know

Most of the time I feel like an average person, but then all of a sudden I'll feel empty. Not happy, not sad, just kind of... lost. I'll feel like I need to cry, but I won't know why and I won't know how and I still won't feel sad somehow. I just curl up on my bed with my dog and brave the storm, but I'm also really good at disguising it, so I can be socializing with my family and they won't notice a single thing. I could be laughing on the outside and still feel completely empty on the inside.

This'll last for hours usually, starting in the evening and dissipating before I wake up the next morning. Happens once every few weeks or so, when it used to happen much less often. Everything I can find on depression sounds different than this. What's going on? Is it anxiety of some sort? I've always thought it was high functioning depression, but recently I've read accounts that sound way different.

I'm not sure if it makes any difference, but I'm a 15 year old female.