Some people have hormone issues following a TBI. Many do not. It is something to consider but, other than thyroid, it is expensive and rarely covered by insurance. Thyroid hormones are worth checking and are more affordable. I think there are 4 thyroid factors to check.

You said, "Unable to concentrate on more than one thing." This is normal and should be something for you to choose to limit. Research shows that trying to multi-task is stressful on even healthy brains. Multi-tasking is grossly over-rated.