Hiya getsome.... I'm really sorry for your losses, I hope you are looking after yourself.
I had 5 (known) miscarriages in all including my sons twin (all my pregnancies were IVF) but the initial thought for our infertility was my husband who has a very very low sperm count.
However, after the 3rd miscarriage it became clear that we needed some tests regarding the whys! I opted to have what are called Chicago Tests - basically I had 87 gallons of blood taken (slight over exaggeration!) and they were sent to a clinic in Chicago who test for all kinds of immune/blood issues and it was discovered that I have a few under lying issues that caused me to A) not conceive at all and B) lose my pregnancies.
I have NK Cells which is very simple layman's terms causes my body to reject 'foreign bodies' such as virus etc including embryos, I have Factor V Leiden which is essentially sticky blood resulting in not enough blood flow to my uterus, I have Homozygous MTHFR a gene mutation that causes my body to not absorb and use B vitamins properly including folic acid and somethings wrong with my ANAs! Altogether, these things were catastrophic with regards to helping me to get and then remain pregnant.
However, all those things had a really simple fix once we knew what was wrong and with high dose folic, clexane injections to thin my blood and steroids to lower my immune system I gave birth to a beautiful little boy.
What I am trying to say in my waffling above is that there are multiple reason why and yes, sometimes there arnt but if I was you I would be broaching the subject of blood tests such as the Chicago Tests I had to hopefully get to the bottom of it.
Ask about them, ask them to tell you about EVERYTHING that is available to you. I had pay for Chicago Tests because I had them done through my IVF clinic but that might not be the case for you.
I wish you all the very best.