Repeat prescription orders are only for medicines which you are taking on a long-term basis. They can't be used for a course of treatment. For instance, even though you might have had a number of prescriptions for urinary infections in the past, it is unlikely that an antibiotic is on a repeat prescription and contact with your usual doctor would be necessary before a prescription would be available.
If you have recently had your medication changed at a hospital visit, your records may not have been updated as a letter takes time to arrive at the surgery so contact with reception would be needed to confirm that the new medication has been added to your list (and just as important that the old medicine deleted if appropriate).
Once you have had 6 repeat prescriptions of your medication, you will need to make an appointment with your doctor to review your medication.