What all medicine having been tried and what doses ? Have you tried any form of therapy ?

Exercise , meditation ,yoga are good ways to improve concentration.Above methods regulate the neurotransmitters and other neuropeptides.for more specific skills you can contact me.all the best.

Antidepressants usually take time. And cognitive effects of depression can persist even after the depressionimproves. So do consult with the doctor and review antidepressant. In addition, Exercise increases endogenous opiates and natural neurtrophic factors like BDNF which promotes growth of neurons in the hippocampus which is responsible for storing memories. Therefore there is no substitute for exercise and following a good sleep wake cycle along with concentration exercises, memory games etc

Why don't you go for therapy session. It will help you Consult with me or any psychologist for therapy and counseling All the best

Concentration problem is the observed and commonly reported symptom of the underlying problem of depression or anxiety. And until you treat the rootcause nothing would help you much. If the drugs have not worked in the past, visit the doctor to know more about the cause and other possible treatment