Two suggestions:
First:
Have an "Add" button that opens a "new" form and have that new form call the same table in a similar form but in "Single Form" and filter to the new record line. You can add a button on this second form that would simply go to the next record, which should save the data entered.
Second:
Have the "Add" button open a similar looking form, but remove all binding from the Text Boxes. Add the code below changing the form and Text Box names to suit your needs. The code below closes then reopens the entry form to make inputting more than one new record easier, but you can set it to go back to your main form.
Code:
Dim dbs As Database, rst As Recordset
Set dbs = CurrentDb
Set rst = dbs.OpenRecordset("Select * from YourTableNameHere")
rst.AddNew
rst!Field1 = Forms!YourEntryFormNameHere!CorrespondingField
rst!Field2 = Forms!YourEntryFormNameHere!CorrespondingField
rst!Field3 = Forms!YourEntryFormNameHere!CorrespondingField
rst!Field4 = Forms!YourEntryFormNameHere!CorrespondingField
Set dbs = Nothing
rst.Update
rst.Close
DoCmd.Close acForm, "YourEntryFormNameHere"
DoCmd.OpenForm "YourEntryFormNameHere"