Beti, it sounds like you're really struggling with this stubborn dandruff, and it's completely understandable to feel frustrated when nothing seems to work. Since you've tried many over-the-counter options, let's consider a few gentle, home-based approaches and then what might be the next step.

For a natural remedy, try applying a paste of fresh curd (dahi) mixed with a tablespoon of lemon juice to your scalp about an hour before shampooing. Curd is soothing and a natural probiotic, while lemon has antifungal properties. Massage it in gently, then rinse thoroughly. Also, ensure your scalp isn't left damp after washing, as moisture can encourage fungal growth. However, if the issue is severe and spreading to your face, it's a strong sign to consult a dermatologist. They can properly diagnose the root cause, which could be a specific fungal infection or a skin condition like seborrheic dermatitis, and prescribe a targeted medicated treatment for lasting relief.