It's ironic that you've used the word 'depressed' to describe your current situation. I say that, because, that might very well be what you are going through right now. I do not want to scare you, but 'Depression' many time manifests with lack of concentration, irritability, indecisiveness, and so on. When this happens, we're lost in a maze and can't seem to figure out what is happening to us. Therefore, it would be teribly ignorant, if you just ignore these symptoms and try to figure out solutions all by yourself. It will end up frustrating you even more. The reasons for this, can be numerous, ranging from your dislike for the subjects you're studying, going through some other stressful situations in your life, relationshio issues, family issues. Whatever the cause is, you need to figure it out, soon. This can be only done by a Psychiatric professional. So kindly consult with a Psychiatrist at the earliest, who will be able to give clear answers for why this is happening, and devise a suitable management plan. I'm sure you'll back to your earlier finctioning level, and better, soon, with the right treatment and guidance. Don't stress, Good luck!

Poor concentration could be related to a wide variety of factors, like fatigue, uninteresting activity, boredome , etc which could be present in any person. For these you can try to employ strategies like taking a break between studies, group studies, using a reading room, making pneumonic etc. It could also be related to many possible physical and psychological factors like poor eyesight, depressive episode, anxiety etc. In such a scenario you would require a thorough evaluation by a physician or a psychiatrist, who will be able to help you by correcting the underlying problem. Hope this helps you...