I have similar symptoms where it's very hard for me to concentrate, like my mind is hitting a wall and I feel mentally exhausted and pushing through it just makes it worse.
For me this is fluctuating, worse when I'm stressed and tired.
A lot of times I find myself losing my train of thought, especially when talking to more than one person at a time, and English being my second language makes it especially hard sometimes as I can't recall a word I'm looking for.
As to your question it is probably hard to tell if you developed this due to concussions or it is caused by you predisposition to these...
I would guess that concussions had something to do with this, but hey, I'm not a doctor