What causes the stage of Trigger finger is relatively unknown. Speculations go as far as gripping a steering wheel over long periods. It's severity is more common to those with Diabetes and by conditions related with Rheumatoid Arthritis. A Steroid injection (Cortisone) into the Flexor Tendon can bring temporary relief and can even provide a cure for some. For others, surgery is necessary.
Stretching and ice can bring some relief.
Get it checked out, it is curable.