Are your studies making you depressed? Is it the workload and the pressure? Maybe you are not sleeping well which can cause poor concentration. How is your diet? Take some time out from your studies, maybe 1 hour each day and do something fun that you really like. Go outside for a while if you can and just breathe in the fresh air. Take a brisk walk and try not to think too hard about any problem. If your case is serious - you need to talk to someone who can give you an objective view. I do hope that things get better.