What could this be ? Please help !?

I have been having problems with my head . This started about three weeks ago when I noticed I was feeling kinda weird . It seems like Im lacking the ability to concentrate or something . I often catch myself in a daze staring off into into space (day dreaming) . Anyways also , I feel like I am very forgetfull and having trouble with my short term memory . Im also having trouble sleeping at night and once I do fall asleep , I sleep A LOT ! I havent had any head injury's of any sort either . This could just be a mental thing . I might be freaking out a little about this but it's really staring to irritate me . Im 15 years old , I shouldnt be having this problem . If this continues for another week or so , I'ma go to my doctor . Any suggestions on what this might be ? Anything helps guys ! I appreciate it !