Hi Deli...
First, the fact that you know the sounds aren't real is good. Try to keep remembering that. Are you do for a physical any time soon? Can you tell the mom you would like a private conversation with the doc? Self diagnosing is a dangerous thing, there is a LOT of info on the internet, and it's not all accurate. It can make you stressed just reading it. It's also really important that you don't self medicate, that means to stay clear from non prescribed drugs and alcohol. Those things can push you into psychotic behavior quickly.
To answer your question, I was about 19 when it started. I began seeing shadow people at first, then they began speaking to me. I was capable of getting thru college, and marriage and a couple kids without any help. Nobody knew. I hadn't hit 30 yet when it all came to a head. I started obeying the voices, and it crashed relatively quickly at that point.
Find someone to talk to about it. A guidance counselor at school, a youth center, etc. You can even call the Samaritans in your area...find the right number at samaritans.org. Or you can email them: jo@samaritans.org They aren't just for suicide, they are helpful with all sorts of worries.

Peace