There are probably a number of causes, but coffee may be one of them. Don't be radical, but if you're having too much coffee, I'd suggest cutting down to just one coffee in the morning. It will take a bit of effort but may help you concentrate.
I'd suggest gradually cutting down to none. Apparently the alertness and general cognitive enhancing properties of caffeine don't really exist and all that people are noticing is the effect of the caffeine on their caffeine withdrawal symptoms.