I am so sorry about your MMC.
Just on the off-chance that it could help anyone I'm going to post my experiences of TTC with low (and undiagnosed) thyroid levels.
Briefly, my thyroid started to go pfffft while I was working in a very stressful job in 2001-2003. In June 2003 I came off contraception (mirena) with a view to ttc. My thyroid nose-dived further- we'd just moved to Canada in mid-summer and it was 27C yet I was constantly shivery and with goose bumps- impossible to get warm. I spent a year walking 6-10 miles a day in an effort to keep warm, did loads of other exercise- skiing, rollerblading, snow-shoeing, x country skiing, swimming etc, eating normally, yet gained 1 stone in a few weeks after having the mirena out. Came back from Canada after a year 2 stone overweight -which I've never managed to shift since. I was pretty convinced I was hypothyroid as my BBT was 35.6C most of the time, with occasional days just before my period at 36.2C (when I felt much better incidentally). Every single day felt like a struggle to stay warm. I so wished later that I'd been to see a GP in Canada as the North American treatment protocol is a lot less conservative than here. I just thought my body to was re-adjusting to not having the Mirena and my hormones would eventually sort themselves out. I was wrong.
As far as ttc was concerned, my periods weren't normal throughout that year, so although I suspect several very early mc (around the 4-5 week mark) nothing happened in terms of pregnancy. I was becoming crazy what with the failing to conceive and the thyroid issues. I honestly thought I was going mad at times.
In 2005 after struggling through yet another year of life I went to my GP. Had a thyroid test. TSH was 4.79, which my GP declared "normal" and tried instead to put me on antidepressants (because clearly what a woman whose BBT is so low that nothing works properly any more needs is antidepressants ). I walked out of his surgery and never went back to him.
Late in 2005 I started running in an effort to keep warm - and it was a BIG effort most of the time. I still didn't lose any weight but I did start to feel a lot better. And then bugger me if I didn't get pregnant. Had problems with bleeding even from before the pregnancy was confirmed, which continued for the next three months. I was hospitalised twice with heavy bleeding and enormous pain. Every time the baby was fine, wriggling away in a sea of blood. Two days before the dating scan I just felt that the baby had died. Can't explain it- I just knew. At the dating scan, it had died (at 12 w 6d). MMC.
I decided to pursue the thyroid problem things again. Went back to GP. TSH was by chance on that day just a smidge over 5, so I was referred to an endocrinologist. By the day of the appointment, it was back to 4.something. So they said "subclinical" and refused to treat and discharged me. (you can imagine how I was by then).
Throughout this time I was having mc at 4-5 weeks (what they call "chemical" pregnancies). I bought a bulk job of sensitive sticks so I have a rough idea how many times I was pregnant in the years 2005-late 2008 and it's well into double figures. I calculate that I was pregnant in probably 1 out every three cycles.
In 2008 I started running again. And bugger me if I didn't get pregnant again. At 40. And this one stayed by some miracle. At 11 weeks I saw a lovely obstetrician specialising in endocrine stuff who said "if you have symptoms of hypothyroid then you are not subclinical" and put me on levothyroxine and treated me through the pregnancy. It absolutely changed my life- in fact I have my life back. And I have a gorgeous, gorgeous child into the bargain. I will never be thankful enough to that obstetrician (and also to the one who saved me and DD3 later!).
So, 6 years ttc, to the edge of madness (and beyond at times), 12-15 early mc and one 2nd trimester one, all to avoid the cost of £1.24/month to the NHS. I wish I had been a lot more assertive with my GP a lot earlier.
"If you have symptoms, you are not subclinical" should be be pasted up on every GP's wall imo. And they should bloody well stop trying to put people on ADs when the problem is something else entirely.
Sorry, it's actually quite long.