I'm sorry you're going through this, OP.
To answer your question, the reason why doctors give such conflicting advice about recurrent miscarriage is because it's an area which is difficult to research and difficult to treat. There also isn't much incentive to do so because the vast majority of women with recurrent miscarriage will go on to have a baby if they just keep trying. That's not to say there isn't a problem, just that eventually they'll get "lucky" and one will stick. I realise that isn't much comfort for someone where you are right now.
The other problem is that it can be caused by really diverse problems such as a hormonal imbalance, a blood clotting disorder, a genetic mutation, scarring in the uterus, structural problems in the uterus, poor egg quality, poor sperm quality and probably other things yet to be discovered. This makes research difficult because if a woman hasn't been diagnosed with a particular problem, researchers would be comparing a group of women with completely different medical problems, all leading to the same outcome.
I was where you are this time three years ago. I went to see a new doctor in the hope that he could help. Unfortunately I am in France so giving you his name won't be much help.
The first thing he did was run all the blood tests again to check for thyroid issues, clotting disorders, the MTHFR mutation, translocation etc. My husband also did the latter two tests and a sperm analysis. We both had the MTHFR mutation and were put on methylfolate.
The doctor also did a hysteroscopy to check for structural issues in my uterus, which ther were none, and a full fertility checkup. This involved blood tests on day 3 of my cycle to check my FSH, LH and estradiol levels, and 7 days after ovulation to check my progesterone levels, as well as an ultrasound in the second week of my cycle to check my antral follicle count. Based on this he concluded that I was not approaching menopause and so my issue was unlikely to be egg quality.
I did have a thin endometrium, for which I was prescribed pentoxyfylline and high strength vitamin E. However, the evidence for this is quite poor. It's one of those "can't hurt, might help" things. Separately, I started drinking a lot of grapefruit juice in the second week of my cycle. Some women swear by this for egg white cervical mucus, and since the rationale behind that is that it boosts estrogen levels, I figured that if it works for EWCM it should also help thicken the endometrium.
I also had an endometrial biopsy to check for abnormal natural killer cells, but the results came back normal.
Having failed to find a cause, my doctor explained that there were a number of things we could try, including a couple of clinical trials, but if absolutely nothing worked the last resort would be to do IVF with preimplantation genetic screening so we could be 100% sure the embryo was normal.
I did one cycle on intralipids and had another chemical pregnancy, so we didn't try that again. That was my 5th loss, as I had already had 4 before I went to see this doctor.
We then did a cycle where I had ultrasounds every couple of days from day 10 of my cycle, and when my follicle looked just the right size, we triggered my ovulation with Ovitrelle, which is HCG, the pregnancy hormone. The trigger shot is a standard part of the drug protocol for both IVF and IUI. I did two further half doses of Ovitrelle at 3 and 6 days post ovulation, and took progesterone after ovulation. There isn't much research regarding using HCG to support early pregnancy, but it is a cheap and low intervention option and my doctor said he'd had some good results.
Anyway, I got pregnant again on that cycle, my 6th pregnancy, and that time it was successful. I did the same thing again a year after my son was born and it was successful again, so I ended up with two children from my 6th and 7th pregnancies, and a 21 age gap between them.
In your case I think it is important to do all the testing that is available to make sure there isn't a known cause which has been overlooked. But bear in mind that all the testing in the world won't necessarily produce an answer. It didn't in my case. Once you've done all that, you need to find a doctor with a game plan, meaning a plan for what to try and in which order. Basically, someone who isn't going to give up until you get your baby.
Good luck, and feel free to PM me if you have any questions.