I've heard of ladies being tested for Natural Killer Cells.

I'm not 100% sure what this involves but natural killer cells basically kill of the embryos in your uterus (or something to that effect).
It can be treated though. A friend of mine knows someone who had lots of failed IVF's and was investigate for that, was found to have very high levels, had it treated and is expecting any day now.

Is there any way you can also maybe see another Dr? I read somewhere that after 3 failed cycles, it might be time for a change in FS.

Hope you get your answers and your BFP really soon hun.
Sue xxx