Iui failed 4 times

Sree
Hi, my fourth <a href="https://glowing.com/glow-fertility-program">iui</a> too failed, doctor said I have good follicles, regular periods,good ovulation, proper egg release, endometriosis thickness is good, everything is fine in me, but four times my <a href="https://glowing.com/glow-fertility-program">IUI</a> failed, I am so depressed, what to do now, why it's failing, what's the reason, can anyone help me out please