Pivot Table: Columns not selectable as fields

Good Afternoon All,

I'm using a spreadsheet I made in Excel 2007 to create a Pivot Table, but I'm running into problems when trying to find/select the proper fields.

Here is how my spreadsheet is formatted:

--------(Column A)----------(Column B)-------------(Column C)--------
(sub a)(sub a)(sub a)(sub b)(sub b)(sub b)(sub c)(sub c) (sub c)


As you can see, I'm using larger, merged Columns and individual sub sections. This helps me organize the spreadsheet better, but when trying to run a pivot table only the sub sections appear as selectable fields.

How do I find and add the larger columns to my pivot table's list of selectable fields?

Please, if I can provide anymore information to help clarify what my issue is, let me know, because the way I'm explaining my issue is a bit confusing. Thanks for your time and have a blessed day!

-Oaki