I think you have had some good advice on this thread. I have been through this and I do think the answer is a combination of stuff. I now have decent hair and you can't see my scalp any more. Mine is probably hereditary, but the treatments below have definitely helped it.
Definitely see a trichologist.Yes it will have to be private, but it is worth it. Doctors are not trained about hair health and their "normal" limits are not good enough for hair. The trichologist should be able to arrange blood tests which are aimed at all the markers for good hair growth.
I also saw a specialist nutritionist and her advice boiled down to protein at each meal and red meat at least twice a week. To grow good hair you need lots of protein, which can come from pulses and nuts as well as meat and fish. Dairy products provide some protein, but it is less effective for hair growth. Ideally aim for meat, eggs or fish at each meal plus a vegetable form of protein. Hair also needs LOTS of iron. She told me to aim for ferritin of 80, but certainly high seventies and I now achieve this despite some lovely heavy menopausal periods. Consciously include plenty of natural iron sources in your diet: sunflower seeds, nuts and dark leafy greens. Red meat does provide iron in its most usable form so don't skip that. Minced beef as spaghetti bolognese or similar is fine, it doesn't have to be steak. Iron in supplements helps but does not substitute for the right diet. Also eat oily fish like salmon or mackerel at least once a week.
No trauma. The body sees hair as inessential so it is the first thing to be dumped if you are ill or starve yourself. I lost a lot of hair three months after having pneumonia for example, but it grew back (there is a lag of 2-3 months in most positive or negative hair reactions). Absolutely no crash diets for the same reason. You can diet but take it slow and make sure you maximise your nutrients.
Yes to minoxidil. It is not a magic solution but it does stop further loss and over time does promote hair growth. I use 5% and stick it on every night after cleaning my teeth. It's just part of my evening routine now.
A good hair and nails vitamin. I have tried pretty much all of them and the one which works best for me is Perfectil Max skin hair and nails. I do see a difference in both my hair and nails when I take it. I also take a daily saw palmetto capsule as an anti androgen.
Don't just give up and cut all your hair off, there are things you can do to make a difference. One of the worst aspects of hair loss is feeling helpless, but I suspect that in three-six months you could make a big difference.