I was 36 when I had dd and it had taken 6 years from my 'first' pregnancy, though I suspect I had my first miscarriage (undetected) when I was in my 20's (but I never count it - wasn't with dh, so I've never even talked about it to him).
You're both young, which is in your favour. I had my results back from the clinic and was told there was nothing awry. Possibly, I had a slight hormone imbalance but nothing that should have affected conception/pg.
For my successful pregnancy I had hormone injections from week 6 to week 14, but when I had my 4th pg I was told that had proven to be an ineffectual treatment!!! So who knows what was different about pg3 vs the others???
I asked my doctor to refer me to the recurrent miscarriage clinic after the third. I live in Sheffield and they have a great women's hospital. Hopefully, there will be somewhere close to you. It makes the testing side of things easier. But we had referrals from all over the UK, so they clearly can deal with distance when required.
If you attend Recurrent Miscarriage Clinic, you have a higher chance of carrying your pregnancy through to it's end, though they don't know why. 9 times out of 10 it's not because of medical treatment, they just think it's because of the care/lack of anxiety (comparatively) involved.
I think that's why my last miscarriage hit me so hard. I'd done it once, fgs...what was wrong now??? So I can relate to how you ladies feel, even though I had my child after 3 mcs and never thought she'd arrive!
I do think it can be harder when you have a child, too, because you know what you're missing out on. I do treasure dd all the more having worked so dammed hard to get her, then failing to provide her with sibling.
Have a good weekend and you have each other now. It helps to have people who understand how you feel...and mumsnet is ideal for that. Take care both.