Hi there, and sorry you are having so much trouble.
I am 5 1/2 years post concussion and it was not as bad as yours. That said, I know full well the depression and feelings of irritability and frustration you are experiencing. You will probably need a lot more rest, take as much time off of work as you can to let your brain heal, and be kind to yourself.
Recovering from a traumatic brain injury is a slow process. You may have three steps forward and two back.
The emotional side of it can be tumultuous. Are you seeing a neurologist? You may need to go on medication to regulate your mood for awhile during the recovery period.
Rest, rest rest!! I can't emphasize that too much. I was off work for nearly two years, and I still have set backs all this time later. Your individual situation is just that, yours, and no one can predict how your own path of recovery is going to flow. But you will get better.
Take care, write again.
Laura