I assume you mean you're taking an antidepressant and you feel it has affected your ability to focus and concentrate? If so, if the drug is new to you this might go away. If it's not new to you and this has been going on for awhile, it might be that this med isn't the right one for you. You might want to bring this up with your psychiatrist.
Depression will definitely mess up your memory. It does mine. Need to get help for the depression or it will put a major strain on your brain in the long run. Please let us know how u are doing.
You could just talk to your psychiatrist, and may be you will feel better with time? Or if this has been going on from a long time, then may be you should change your medicine.