Hi SarahLou. I had a few infections sequentially and lost lots of my hair earlier in the year, Regaine helped me get it back, it worked fantastically, but I had to give it up as it triggered some kind of enzyme-related acid reflux
I have however found that my hair's improved a bit (hairline a bit better) on continuous combined HRT. Oestradiol alone makes me shed hair, even Vagifem, but any kind of progesterone, although tiring, seems to stop this. It'll never be as thick as it was when I was young though, although Regaine gave me back my 20-something thickness for a short while. Nice while it lasted!
Another friend of mine found her hair improved on HRT, but some people have a different experience. Low iron also seems to cause hair loss, or thyroid issues, but it sounds like you're having tests for all these? Or if you're struggling to sleep at night could it be stress-related?