Is Tamoxifen working? Endoxifen Blood Test Numbers are Off!

I'm on my 4th year of Tamoxifen. I posted previously that my MO did a hormone test (including estradiol) to determine if I was pre-menopausal. Based upon the results and the concerns voiced by my Ob/Gyn that my estradiol numbers were too high, my MO suggested we try lowering the dose of Tamoxifen from 20mg to 10mg. She then added for me do a blood test for Endoxifen levels to make sure that the Tamoxifen was working at the lower dose. My Endoxifen level ended up being too low. We then decided to increase my dose to 15mg for a month, at the end of which then repeat the Endoxifen level test. I got the exact same result as the previous time! At this point, I found an article that said that higher levels of Curcumin (or Turmeric) could interfere with Tamoxifen effectiveness. Even though I was only on 750mg (which is lower than used in the study), I was taking it with Tamoxifen every night. So I stopped the Curcumin for 6 weeks and then re-tested the Endoxifen levels. This time my test came back even *lower* than the previous 2 times! Huh?! Right now I'm waiting to hear back from my MO about the latest lab results, but I'm really at a loss as why my Endoxifen levels would go down again! After my first Endoxifen test result came back low, my dietician suggested that I do the CYP2D6 enzyme test to see if I'm a bad metabolizer of Tamoxifen, but my MO said that insurance may not cover the test, the test is not so reliable, and that the Endoxifen blood test achieves the same result. I'm wondering if this Endoxifen test isn't so reliable too? Any suggestions on what to try next??