Hi Longest, so sorry you're here...
I think it is such a postcode lottery tbh. I was referred by my GP once I hit 3 mcs, but I had a general Gynae consultant at first, who referred me on to someone with more specialism in the area. I continued to have mcs (now have a dizzy five under my belt), and it seemed that I was referred for more tests after each one.
I found that the service I received improved dramatically once I was seen as an interesting case, which I found fucking frustrating to be frank.
The route that a lot of us seem to have taken is to pursue all the NHS tests, where they look at hormone levels, clotting issues and infections etc, scan to make sure your uterus and ovaries are in the right place/size etc, and may also offer karyotyping of you both to look for any chromosome issues you may have. They only find a cause this way in 50% of cases, and if nothing is found (like me) then you'll be told you're lucky!
Quite a few of us here have now explored NK cell testing, which is not NHS treatment, so you have to pay, but that feels a bit last chance saloon for some of us.
The cumulative effect of all the mcs can really take it out of you, both physically and emotionally, and I have benefitted enormously by taking some time out of ttc. This helps with all the testing too, as they can get some nice clear results.
Hope you and all our newbies find the help and support you need. We are a friendly, if slightly jaded and world weary, bunch.
Tiny only a few more days and it's back to a good book 