Risperidone is an atypical (second generation) antipsychotic. Vyvanse (lisdexamfetamine) is a stimulant. Zoloft (sertraline) is an anti-depressant. Methylphenidate is a stimulant. Your son is taking two stimulant medications which are generally indicated for ADHD, and sertraline, an anti-depressant, indicated for the treatment of depression. Risperidone is typically indicated for bipolar disorder, or schizophrenia, however, it may have additional uses as well. Stimulant medications such as methylphenidate may increase the risk for new-onset psychosis; patients must be monitored for symptoms of aggression or hostility. Regarding the antipsychotic medication, risperidone, this drug has a side effect of causing a reduced attention span in less than 4% of patients.
I do not have enough information available to determine the most appropriate course of treatment for your son, but I would recommend you review his current medication regimen with a psychiatrist if you feel his symptoms are not currently being well-controlled.