[AccessD] Many to One to Many to Many form design problem

Hello,

I am hitting the wall on a form design. 
The database is supposed to track medications dispensed by a doctor's
office.
There are four tables:
tblPatient
-       PatientID           - PK
-       PatientName
-       Etc
tblDrug
-       DrugID              - PK
-       Drug Name
-       Strength
-       Type (Capsule, Liquid, etc)
tblDrugLot
-       DrugLotID        - PK
-       DrugID           - FK related to tblDrug
-       Lot Number
-       Manufacturer
-       Expiration Date
tblTransaction
-       TransactionID    - PK
-       PatientID        - FK related to tblPatient
-       DrugID           - FK related to tblDrug
-       Transaction Date
-       Units Ordered
-       Units Received
-       Units Shrink
-       Units Dispensed


A transaction can be medication coming in from the supplier or going out to
a patient.

I am trying to build a transaction form that will allow me to identify not
only what drug, but what lot, came in or went out.


TIA,
Kevin