Amphetamines don't cause schizophrenia, however they can make symptoms more pronounced in individuals who already have the disorder.
I don't know your age, but schizophrenia tends to begin to manifest in late adolescence to early adulthood, so its likely just a coincidence. If you're not already, I would strongly encourage you to find a good psychiatrist and work with him to find medications to help you. Schizophrenia can be well-managed with medications, so long as you will trust your doctor and be willing to work with him to find a good treatment program.
Since I've answered your question, I'm going to go ahead and close this. Please check The Dark Side forum for more support and information about dealing with schizophrenia.