Having a pain in the joint of my left hand of the middle finger?

Many Possibilities: Could be many different causes, which include simple reasons like tendon or ligament strain from overuse (i.e. Computer overuse) to systemic causes.Most often it is an overuse issue or injury, but red flags to consider are swelling, morning aches, and having other joint involvement. If it persists would recommend seeing a rheumatologist or an orthopedic hand surgeon for an evaluation.

Tendon Inflammation: There are multiple causes of finger/joint pain. Given your age and no history of trauma, nor arthritic problems, the most likely cause is a trigger finger or tendonitis (swollen tendon). Ask yourself, ifyour pain is on the back of the knuckle, worse in the morning, and painful with flexing the finger, and if there is tenderness in the palm over the tendon. A hand surgeon can help make diagnosis.