Swollen ring finger on left hand. No joint pain just stiffness. No other fingers hurt. Both hand and wrist feel fine. No redness. Any ideas?

Remove ring, if any. If you are wearing ring on the affected finger, you try taking it off and going without for a couple of weeks.
Swollen finger. Most likely it was an insect bite or an injury that was not remembered. You have ruled out a systemic arthritis. Tumors of the hand are rare. You are too young for most other problems with fingernails. They would be obvious and painful. Occasionally, you can see tiny pin point sites of the bite. Use a magnifier. Don't be surprised if it itches. Warm soaks may help clear the toxins.