That's actually really good that she's testing you for that Abs!
I don't know if that's a standard test for infertility or other things too, but I've had that included in my recurrent miscarriage testing. One major thing that can cause recurrent miscarriage or recurrent implantation failure are autoimmune diseases - coeliac disease is one of them. From what I understand, it's something to do with the inflammatory reaction they cause that makes your body attack itself and therefore can also interfere with your pregnancy - either by antibodies attacking the pregnancy like it's a foreign body, or causing your blood to clot more. That's why baby aspirin is usually a first line treatment. I'd even ask your GP if they think it's worth going on baby aspirin - either all the time, or once you get a BFP. I've never read about any bad side effects with baby aspirin - although I bet other medical stuff could possible overlap with it if you know what I mean.
You probably also got tested for blood clotting disorders, lupus and thyroid issues too (although thyroid antibodies are sometimes missed).
Oh and you're totally right in thinking that it could just be bad luck! The thing about my miscarriages that has the red flags is that the babies had normal chromosomes. Obviously with really early losses it's just impossible to test for that, but that probably is the most likely cause as I think chromosomal issues make up something like 80% of 1st tri miscarriages. To me chromosomal issues really are bad luck - the odds of it happening go up as you get older or if you yourself have undetected chromosomal issues, but it also randomly happens to young couples too.
