It just occurred to me...you said that you were off PPI's for just 3 days prior to the test. While I know some docs will do the test while patients are on PPI's, the standard procedure is to be off PPI's for a minimum of 7 days prior to the test.
If you scroll down on the page linked below, you will see the test prep that is more standard:my.clevelandclinic.org/services/esophageal_ph_test/hic_24-hour_esophageal_ph_test.aspx
It does state that a doctor may want you to continue with a specific med during testing in order to determine its effectiveness, but it seems to me if that were the case the doc would have let you stay on the meds altogether.
In any case, it seems to me that the results could be skewed if there are some residual PPI or H2Blocker in your system. just a thought...