Why can’t I concentrate?

Hi, 

My dad passes away just over three months ago after going from fighting fit (travelling the world) to saying his last words within a space of 9-10 months. We were very very close and I miss him dearly. 
 

On the whole I am finding things okay but I am Struggling at work. I don't think things are effecting me but clearly they are. I am less effective at my job (I'm a teacher) and I mainly feel like my head is a blur/fuzzy. Just wondering if anyone else feels this??? 
 

Thanks xx