I have been having a similar issue with my estradiol levels, though I inject (IM). It's been very worrisome as my levels also have been all over the place, both before and after GCS to the point where my dr is threatening to put me on pills which I adamantly don't want to do due to an issue I have had with my kidneys in the past.
I am very interested to see if you figure out what's going on. From a blood testing perspective, are your blood draws always at the same point in whatever cycle you are on (daily, weekly, whatever)?