Considering mysite.com is a root of public_html
Most Important: Before you go further, take backup of entire Q2A site source and database.
so move or rename your subdomain directory (qa.mysite.com) t0 QA and place q2a source in that.
in the database (phpmyadmin) goto qa_options table and find the title site_url and change it from http://qa.mysite.com to http://mysite.com/qa
You might have to modify.htaccess for your root site if it doesn't load QA site and redirect to 404
Once all set, it is advisable to recalculate everything from Admin > Stats page
Additionally, try to share your question on the Group to let more people know the issue out of the Q2A. I am sharing now for you :)