Concentration issue. Coming in my mind!

Hi, based on your description it seems like you are preoccupied with your thoughts. Since how long have been feeling this way? Are you able to sleep well at nights? You need to relax and clear your mind of everything and then decide on your priorities. If work is where you have to be then you need to take couple of deep breathes and start using self suggestions like 'you have to focus on your desk' or ' you need to finish this task before thinking anything else'. This is rough sketch of how you can use self suggestions to get positive outcome. You can also try listening to some instrumental music which can dissolve the noise around you and help you focus on your work more feeling relaxed at the same time.