Two ideas for the fingernail....

1) yeast (candida)... may respond to liquid clotrimazole (Lotrimin) applied topically. You most likely would have to special order this at your pharmacy. They don't put it on the shelves anymore.
Twice a day --a few drops.
A swollen joint should be seen... could be some other infectious process IMO.

2) Psoriasis.... this would make the joint swell as well. But only one finger is odd... others would be typically affected.
My husband's grandfather had psoriasis of the nails... really icky looking!

The fact that you have only one affected, suggests a local problem, and not systemic. If many or all were affected that could be something else.

I smashed one finger with a rock last fall by accident working on the rock garden. Its nail is not doing well. I suspect it will not be normal much longer.
It has a long vertical indentation in it, and now it is splitting alot. It throbs sometimes in the night. There is a small lump above the cuticle, but otherwise it looks normal. It is the same finger my father smashed in a car door when I was young. Its never been normal looking...so I guess now it is dying too. It was broken at the first joint, then, and is a little deformed looking.