Thin Endometrium. In this issue?

I have been struggling with thin endometrium for the past year. In every cycle, I have tried multiple approaches to improve my endometrial thickness, including: 1. High-dose estrogen 2. Letrozole for five days followed by estrogen 3. Tamoxifen along with acupuncture I am getting max 5.6-5.9 mm. I have also undergone multiple abortions and D&Cs, as well as a laparoscopy for hyperplasia but none of these have resulted in sufficient endometrial growth. We have embryos ready for transfer, but due to persistently thin endometrium, we have not been able to proceed with the embryo transfer. Please help me find a solution to achieve adequate endometrial thickness. Are there any advanced treatments or doctors who specialize in this issue?