i happened to fall from a bike and my head was injured, i became unconscious for about an hour

i'm 23yrs old,about 4years ago i happened to fall from a bike and my head was injured,i became an conscious for about an hour,after regaining my conscious,i experienced confusion and and i could hardly make a speech(just stammering) and i could not remember what had happened,i visited a doctor and an x-ray was done but the skull was normal,CT scan showed there was no brain damage,but sometimes i feel as if my brain blocked,sometimes i stammer,and i experience memory problem(taking long to process,something i know like u can ask where i come from but i take long time to remember the name of that place),poor concentration,sometimes dizzness especially when i run for short distance,any body having an idea what might be the problem