weak memory and concentration are a result of stress
n strain..and pressure
if there are any causative factor try to eliminate them from your life..
medicines will be of great help in healing process..
try to destress yourself.. do not exert... if you are not in a mood to study avoid it for some time..
make youself happy n entertained take a break.. get refreshed and you will see the results
drink lots of water and juices hv a healthy diet with salads and veggies..
notice at what time you are best at your concentration .
take adequate rest and sleep..
wishing you good health..