Since a customer has many prescriptions, that's a one-to-many relationship
tblCustomerPrescriptions
-pkCustPresID primary key, autonumber
-fkCustomerID foreign key to tblCustomers
-PrescriptionNumber
-PresValue (value of the prescription)
Since a prescription has a time for when it is valid assuming a start and end date, that is also a one-to-many relationship. So for each prescription you will have 2 records in the following table corresponding to a beginning date and end date.
tblCustomerPrescriptionPeriod
-pkCustPresPeriodID primary key, autonumber
-fkCustPresID foreign key to tblCustomerPrescriptions
-dteValid
-datetype (start or end)
Others might put start and end date fields in the tblCustomerPrescriptions table, but technically speaking it would violate normalization rules. I'll leave that one to you.
Initially I was thinking that you would not tie a particular prescription to an order, but if you must provide traceablity to public health officials then you probably would need to tie specific prescriptions to an order. Assuming that a customer could conceivably have multiple prescriptions open at a time and that the customer may apply more than one prescription to an order, then you would need a juction table.
tblOrderPrescriptions
-pkOrderPrescriptions
-fkOrderID foreign key to tblOrders
-fkCustPresID foreign key to tblCustomerPrescriptions
-AppliedAmount