Coralee, 40 mgs of Nexium is actually at the higher end of the PPI dosage usually prescribed for GERD. That is what I am taking as well, and one doctor described me as "maxed out" in terms of dosage. You might encounter some people who take more than that, but they are usually exceptional cases in terms of serverity. (Some individuals supplement their PPI by occasionally taking an H2 blocker like Tagament or Pepcid to avoid "breakthrough" reflux.) If your PPI is not working after 4 weeks or so, consider bringing up the matter with your MD.
Truly hope you feel better soon.