could be a wicklow.

get some permanganate of potash from the chemist. use an old cup, because this stuff leaves a brown stain.

put a quarter of teaspoon full of the potash in the cup. Fill the cup with hot water (boiling, but wait for it to cool down a little). The liquid should be purple.

Immerse the sore finger tip for as long as you can stand. Your finger will be stained brown. Repeat when you can face the idea.

Usually by the the third time you do this, just by pressing the fingernail, a pearl of white pus will come out.

the next day you finger will not hurt - although it will still be brown for a few days.