WEll it would help if you stated what the error message was, but my guess is that SQL statement wouldnt work on any database i know, including oracle, if it did, then it executed it wrong.
your first value you are inserting, which is a subquery, in the FROM query, Access expects a list of tables after the FROM clause, in this case access is gonna look for the tables Orders, Customer_Name, Doctor_Name, Medication_Name, Medication_Amount, Order_Date, "Entered" which I'm gonna guess a mistake because most of those look like field names not table names, the last being a explicit string, which im sure isnt allowed as a table name.
INSERT INTO Orders VALUES (SELECT MAX (Order_ID) + 1 FROM Orders, Customer_Name, Doctor_Name, Medication_Name, Medication_Amount, Order_Date, "Entered"

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