Hair loss and poor hair quality after a severe illness are quite common and are often due to a condition called telogen effluvium, where stress from fever, illness, or nutritional deficiency (like low vitamin D) pushes hair into a shedding phase. Even after recovery, hair may remain thin, dry, and frizzy for some time. Since your vitamin D has been treated and body pain improved, the remaining issues could be due to ongoing nutritional gaps (iron, vitamin B12, protein), stress, or hair damage from products or the environment. The best approach is to focus on overall health: eat a balanced diet rich in protein (eggs, pulses, nuts), iron (green leafy vegetables), and vitamins, continue vitamin D as advised, and consider checking iron and B12 levels if not already done. Use a mild shampoo, regular oiling, and avoid harsh treatments or frequent heat styling; patience is important, as hair regrowth usually takes 3-6 months. Hair supplements (like biotin or combination tablets) may help, but should be taken after medical advice. If hair thinning persists or worsens, consult a dermatologist to rule out other causes like hormonal imbalance or scalp conditions.