Hey, have you been tested for Natural Killer Cells? I don't know a huge about about this but a good mate of mine got tested for this because she had also had 6 failed transfers.
She didn't actually have any but her Dr tested a few other women in his clinic with high numbers of failed transfers and both of those women had huge levels of NK cells. He treated them and they are both now pregnant.

Just a thought. As I say, I don't know a huge amount about it but when people say they've had a lot of failed transfers for no apparent reason, I immediately think of this.

Good luck
Sue xx