I have a thickening and yellowish nails which is...

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What is the treatment of yellowish discoloration of nails?

In this case you need to consult dermatologist to examine you and treat you. Mostly this is fungal infection that needs management with antifungal meds. If this is not fungal then it might be other skin or nail lesion that is why you need doctor to examine you. Doctor might use microscope to examine nail and nail bed.
Management is guided by cause and nail removal is one of choices. In general I recommend to consult a dermatologist.
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