Look at the string you generate:
SELECT tblVisit.PatientID, tblPatients.Firstname, tblPatients.LastnameDateDiff('yyyy',[tblPatients]![Birthday],Now()) AS Age, tblVisit.[Date Visit]tblVisit.Diagnosis[First Name] & ' ' & [Last Name] AS [Prescriber Names] FROM tblPatients INNER JOIN (tblDoctor INNER JOIN tblVisit ON tblDoctor.DoctorID = tblVisit.Do
ctorID) ON tblPatients.PatientID = tblVisit.PatientIDWHERE [Firstname] = 'Keyword'
Does that look like valid SQL to you?
You need to sit down and work out what query you are trying to send to SQL, then "fill in the blanks" for the specific data you want. What you have isn't valid and I have no idea what you are trying to do!
Add to that: Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.
When you concatenate strings, you cause problems because SQL receives commands like:
SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'
The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:
SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;
Which SQL sees as three separate commands:
SELECT * FROM MyTable WHERE StreetAddress = 'x';
A perfectly valid SELECT
DROP TABLE MyTable;
A perfectly valid "delete the table" command
And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.
So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?