Sorry to hear about about your losses.
I have no success story to share, unfortunately, but plenty others on here have!
If you have had 3 mcs, you are eligible for investigations on the NHS as to why this might be happening. These usually include a chromosome analysis of you and your partner, checking your progesterone levels at different points in your cycle (usually on day 3-5 and on day 21, depending on when you ovulate), and analysis of the pregnancy tissue that you passed (if it could be retrieved). Have you been offered/done this?
They should def check your hormone levels, there is no other way to find out if they are OK, no matter what your doctor thinks. Sometimes, low progesterone is the problem, which can be helped with the pessaries.
There have been quite a few success stories from people on here that have been tested for NK cell levels, following recurring mcs - this is an immune issue that might be treatable with steroids.
Sadly, there is no guarantee whatsoever that it won't happen again, regardless of any tests they do or what they find. Age is a factor of which you need to be aware.
With my 3rd mc, it was a spontaneous mutation that was non-viable, and there is nothing that can be done to prevent that from happening.
Having said that, there is nothing to say either that it will happen again, there are so many women who have been in the same situation as you and gone to have healthy babies, so don't give up hope!