I have been having the same issues. I had a professor/mentor tell me the same thing about the "brain injury." He actually equated my level to that of after a stroke, only without the speaking issue (although I evidently do stumble over my words.) I honestly hadn't even noticed it until my teacher suggested it as a reason for my low test grades, which were A's and B's before my surgery. Then I realized I couldn't remember the day before, let alone my previous semester or classes. Now I have trouble remembering things a week later unless I do it day in and day out.
Anywho, I have focused my attentions by writing notes, very detailed, and by using "cozi" online to keep track of dates. It also helps because other people can log in to the account and put in dates so I don't forget to do it, and my boyfriend can put things on our shopping list, etc. there are also post it notes everywhere in my apartment. And the dashboard of my car.
I'm glad to know I'm not alone in my erratic behavior, and not losing my mind at 22.