Strictly speaking, a psychologist is a psychiatrist minus the prescription medication. Whereas psychiatrists are primarily trained doctors who can prescribe medicines alongside therapy, psychologists use non-medicated therapeutic means to help the patient.
It is important to understand that not all cases require medical help, and that there are instances where medical intervention is helpful. Whether medication is required, can only be ascertained once the case details have been thoroughly examined. In either case, psychotherapy is always useful for better recovery.
Most medicines do not eliminate the root cause of a psychological problem, and offer only superficial relief to the psychosomatic symptoms, which lasts till the prescribed course is.
If you have been on drugs for long, are unsure of whether or not you should consult a doctor (psychiatrist), it is anyway good to check with the psychologist beforehand. After gauging the scope and nature of the case, a psychologist can always refer you to a psychiatrist, should you need medical assistance.