side effect of tegratol

my son is 3 and half years old. he suffers from epilepsy. the doctor recommended to take Depakin but it was not effective as  many seizures happened while taking it so the doctor changes the medicine to tegratol . he has been taking this medicine for one year and a half but i notice that after taking tegratol the boy state deteriorated now he has speech problems , memory problems he couldnot remmber any thing . his concentration become very week , although before taking this medicine he was normal . now he cannot deferentiate between things , animals , etc . i do not know what to do plz help me . plz tell me some doctors recommended to change tegratol to trileotal and others say no they are the same . i m confused and my son's state became horrible plz tell me what to do ? and if there are other medicines that can help in his state plz tell me .