Tamoxifen and continued Uterine Thickening

I have been on Tamoxifen since 2012 and have had 3 episodes of spotting. I began taking it less and less, only 2-3 times a week, and spotted again. I went to the OBGYN and he did a biopsy that came back negative and said to stop completely and come back in 3 months to see if things improved. Well although there is no more spotting my thickness when from 7.2 to 9.9 without being on Tamoxifen. He is suggesting a complete hysterectomy, now I am scared that this is a sign of uterine cancer because of the continued thickening. Has anyone had this happen, should I have a complete hysterectomy?

I had DCIS in 2012, which resulted in mastectomy, and reconstruction.