I've had attention issues since my concussion (2 1/2 years now). I'm a web developer, and as I measure my performance throughout the week - I'm mentally sharper on monday than friday, and also better in the morning than after 8 hours of work.

One of the symptoms is increased difficulty concentrating (that and headaches, uggh....)

Its possible your experiencing the same as me. Either way, you should speak with you dr.