Endometrial shrinkage on day 14

[Frida06]

Hello ladies... here i am with 5 failed ICSI cycles.. depressed and stressed. However made up my mind for my next cycle since I still have frozen embryos. But this time on day 14 of my cycle was a strange observation. Suddenly my endometrial thickness has fallen from 8mm on day 9 to 4mm on day 14.. this was never the case before. Has someone experienced this ? Any input in this regard will be of great help.

PS: I am 28 years old with PCOS