Lack of concentration is one of many symptoms of a disease. One thing often overlooked is when the body is trying to mend itself, we often get run down and often times without knowing it we become physically exhausted and somewhat mal-nourished depending on the circumstances. The body tends to rob Peter to pay Paul to help in the mending process, so the entire body energy reserve is brought down. Worrying about day to day life with a disease and it's complications can be mentally frustrating and stressful also adding to the problem.
Lots of sleep if you can, fluids, exercise and stress relief will work wonders for concentration. It takes a while to find the balance.