What version of FileMaker?
Can you upload a screen shot of your Chart Setup?
Any other details on how you set this up will be helpful.
See attached screenshot
If you open layout setup for this layout, does "show records from" list "Headaches" or a related table?
How did you record the data for this chart? Is each point entered in a different record? If not, how?
Is severity of type Number?
Can you show the options for the Y-Axis? (Your screen shot shows the X-Axis options.)