I have gotten pregnant once & it ended in a miscarriage. I was similar age as you & have not tried to conceive yet since. I generally have very light periods (like, don't even need a pad or tampon), & I was told that my lining may be too thin to let egg attach well & be nourished. I was told that the next time I try, I should risks like stress, sex, too much activity & general unhealthiness. I am normal weight, not thyroid or other disorders, but under a lot of stress usually from my job in neuroscience. I also engaged in sexual activities during 1st trimester, which I know now to avoid next time.
Things I've been doing in the meantime to increase my success in the future is staying more hydrated (to produce more blood), taking vitamins every day (to avoid folic acid deprivation) & also started taking birth control pills which I hope will increase my natural production of estrogen & progesterone in the long run.
One thing that my doctors also told me is next time I should be on a progesterone supplement, as this aids the body in supporting the pregnancy & being in pregnancy mode.
Sorry that you are having such a hard time TTC. I assume I will have similar difficulties in the future. I have not had all that testing that you're talking about, only talked with doctors & have some medical knowledge myself. Good luck going forward! The emotional part of it was the hardest for me. I have tried to de-stress my life since then & take care of my body 100%. :)