After taking 5mg of olanzapine i sleep 12 hours instead of 8, since that time(4 years) i still take 5mg and still sleep 12 hours. is the effect of medication that long? or should i treat it as a separate problem with sleep?

This is not recommended for sleep in US. Go to Drugs.com and read more. Discuss with your Polish Drs

Medication should be managed by your Psychiatrist who could re-evaluate your present medication and possibly recommend another. Have a complete physical exam to know if you have a physical illness causing symptoms. You could be helped by a Clinical Psychologist with expertise in multiple types of psychotherapy. If you are not confident with your Psychiatrist see another for a second opinion.