Hi @Angels4me I'm in a similar boat only it took 4 goes to get preggers the first time, I'm up to my 5th cycle now to get a second (so I guess I was expecting it to be much more of a struggle)
Have you had any chemicals or miscarriages at all? If the blastocysts aren't implanting you might want to have surgery to investigate if you have endometriosis.
Also have you tried changing clinics? Might be good to shake things up a bit.
Also I've heard 'natural killer cells' mentioned a lot on these forums, I don't know if one of the other ladies can give you a bit more detail on that.
I'm sorry you are having such a hard time.