Need implantation advice

I’m currently enrolled in a clinical trial, had 20 eggs retrieved in May and 4 resulting embryos. I’ve had two frozen transfers, both failed. I’m preparing for another try this month. I didn’t respond to estrogen so both my cycles were timed naturally. Does anyone have any advice that helped them after a few failed transfers? I am taking prenatal vitamins, coq10, vitamin d and vitamin e. I had acupuncture for both previous transfers. No alcohol, only drinking minimal amounts of green tea as far as caffeine goes. Any words of wisdom would be helpful.