Maybe 2 other things you should check( if you haven't done for so far):
After you configured Qt you get a report which contains the configuration, make sure mysql is yes (or plugin).
Make sure your .pro file contains the line QT += sql
If you mean with the report the info get after you verify you want to configure qt the yes it always says that mysql: yes or mysqll: plugin
And when i compile a project i always follow the same three steps.
First: qmake -project "QT += sql"
Second: qmake projectname.pro
Third: make
Bookmarks