sometimes symptoms overlap into many different disorders. schizophrenia does include a type of memory problem associated with psychosis, hallucinations, delusions, that come with schizophrenia. your treatment providers may have felt the severity and the type of problems you are having is better explained by your having schizophrenia (one of the diagnostics for dissociative disorders is that the problem can not be better explained by other mental\physical problems)

also many medications that treat schizophrenia do cause side effects that are very similar to having dissociative amnesia and depersonalization derealization disorders.

only your treatment providers can say why they recently diagnosed you with schizophrenia rather than and in conjunction with dissociative disorders.

my suggestion talk with your treatment providers.

and to answer your question whether a person can get diagnosed dissociative disorders and have schizophrenia too...yes but america is now moving away from this dual diagnosis process by making one of the new diagnostic criteria for mental disorders to state that the problems can not be better explained by other mental disorders.. short version when someone is being diagnosed the treatment provider has to look at the symptoms and see whether one or the other diagnosis better explains that problem.

so again to find out why you were not dual diagnosed you will have to talk with your treatment providers who can explain why they felt your problems were schizophrenia not any dissociative disorder.

if you still feel you were wrongly diagnosed you can request a new psychiatric evaluation.