First of all, keep in mind that I am unable to diagnose you because I am unable to examine you, this forum is for educational purposes.
Post-concussive syndrome can be a frusterating and challenging problem. When the brain is injured by a concussion that causes loss of consciousness, it is theorized that axons (like electricial wires in the brain) are sheared and result in dysfunction of multiple areas of the brain without overt structural damage(like would show up on MRI). This dysfunction can lead to personality changes, memory loss, confusion, headaches and sometimes seizures.
When an EEG is negative, this only means you were not having a seizure at the time of the test. You need to have an EEG while you are having your "loss of time" symptoms. This will likely require you be admitted to an epilepsy monitoring unit for 3-5 days, with continous EEG (available at major medical centers).
Ritalin can improve energy, but can also make headaches worse. Due to the severity of migraines in many concussion patients, I would recommend a migraine preventative medication such as elavil, nadolol, topamax, verapamil etc.
After a severe concussion it often takes a team approach between neurologist, psychiatrist and physical/occupational therapist to make the optimum improvement.
I hope this has been helpful.