Hia Charlie, I feel you!
I'm prone to thinning hair too, I have just about enough to cover my head lol, and none spare, especially around the crown.
Good your getting checks, as ferritin, iron, b vitamins deficiency can cause/add to thinning, and obv menopause can contribute also.
I have mentioned on here before that I use Caboki, get on ebay, it bridges the gap by adding keratin fibre to the hair, also caffeine shampoo's help with creating thickness to what you have, but I find once I've box dyed my hair I cant use the caffeine shampoo for at least 5 washes as it doesn't seem to like the dye, and goes limp but ok after that.
Try not to worry too much, I'm sure your beautiful with or without as much hair.
X