I am 15 years old too, and...well, what your telling me seems perfectly normal. Ringing in the ear is caused by loud music, such as a maximum volume on your mp3 player. In other cases, ears can ring once in a while, im not exactly sure why, but they do. Forgetting a word is normal too, it happens to everyone. People sit there and say, "It kind of reminds me of a ...umm... uuhhh..." They cant remember the word. Happens to everyone.
People do convince themselves that they have problems, so they think they hear or feel something. Convincing yourself is also normal, your not the only one that does that.
If someone is watching a movie and they see hundreds of ants crawling on the ground in that movie, then the person who is watching will sometimes "fell" the ants crawling on themselves, and he/she feels like he/she is itchy or something. Its normal.
From what you have told me, everything seems perfectly normal, you shouldn't worry so much, but if this does continue then seeing a doctor wouldn't hurt. I highly doubt you have brain cancer though. Don't worry.