thin endometrium, IVF

During the month of Oocyte Retrieval, my endometrium was 10mm three days after the retrieval, my doctors had all 9 embies frozen because I had Adenomyosis and needed some treatment before transfer. After 2 months of Amendorrhea, I tried for the first time.  I had a hard time reaching required endometrial thickness. It was only 7mm after many dosage of medications.  I failed.  Now I'm trying for the second time.  Same thing happens. It was still 6mm after 17 days of medications.  How could it be? Any suggestions???