This looks like infection of your nail. Mostly fungal. Was there any injury or Any fever or pain ?
Next Steps
Take a course of antibiotics first for 5 days with an antacid. Painkillers if painful.
Tab Augmentin 625mg 1-0-1 after food for 5 days
If you are allergic to Penicillin then please don’t take Augmentin but instead take Tab Cetil 500mg 1-0-1 after food for 5 days
Tab Pan 40mg 1-0-1 before food for days
Tab Signoflam if pain is there on sos basis after food.
Health Tips
If there is no reduction with this then you need to meet a dermatologist for possible nail biopsy and further treatment with appropriate anti-fungal