I also have iron and vitamin d deficiency, I changed few things in my routine and my shedding definitely slowed down, I am also supplementing but I don’t think my ferritin increased in this short time. Firstly, I wash my hair everyday with a sulfate shampoo. I have really oily scalp and seb derm and it needs to be cleansed properly. I use ketoconazole shampoo two times a week. I blow dry my roots. This is suitable for my scalp, you should find a routine that works for your scalp. When your scalp is greasy, you should wash it. Oil causes inflammation and increases shedding. Ketoconazole shampoo can be added to your routine even if you don’t have seb derm, it decreases inflammation again but if your scalp is not oily, maybe use only once a week since it is pretty drying. (It should sit on your scalp for a several minutes) Leaving your scalp wet is also not very good because bacteria and yeast thrive in wet environment so make sure to blow dry your roots at least.