I have the EXACT same problem! I have been diagnosed with dysthymia, but not ADD or ADHD. My grades made the same drops yours did right about when I started to go through puberty. First from A's to B's and C's... then the last few years I've started hitting D's and E's.
I'd say follow your own advice you gave me... We can go see a doctor and get tested/get medication together
((((((nirvanaf909)))))