I've been suffering from very painful joint and knuckle on the left hand, ring finger for about three weeks. i am unable to even open or close my hand?

This requires: an in person evaluation, diagnosis and specific treatment . You are describing a NUMBER of POSSIBLE arthritic disorders including BUT NOT LIMITED TO Rheumatoid Arthritis, Osteoarthritis, Psoriatic Arthritis, and REPETITIVE STRAIN/SPRAIN disorderts of the hands! WARM SOAKS using rubber balls and SQUEEZING gently may give you some symptomatic relief.... until you can have proper testing &diagnosis