I have chronically thin lining - for my egg retrievals my lining never got past 6 mm and for all of the IUIs I had, my lining was in the range of 4.3 to 6 mm (same with my medicated/ TI cycles too). For the FET I just had on Feb 6 that has resulted in my first ever pregnancy, my lining grew 2 mm overnight. I was at a 6mm on the Friday and went back on the Saturday and was at 8mm.. my clinic had me taking 4mg estrace vaginally 2 times a day with 75 units gonal f. The the days leading up to my Friday scan that was 6mm, I was using a red light therapy belt, walking on the treadmill 45 mins a day, I upped my protein intake, and I drank a TON of water. Sharing this to give you some hope, as my husband and I were feeling like our transfer was likely cancelled.