I felt sprain type feeling in wrist & inner forearm yesterday & by evening, if i bend my thumb inward to hand, i have pain and discomfort in inner arm?

Tendonitis: It sounds as if you have a tendonitis of the wrist flexor muscles. Think about what you might have done yesterday in terms of sports or possibly any lifting (weed wacking, painting, spring cleaning, etc). I would take some nsaid, do some gently stretching exercises for your wrist by stretching the wrist backwards. You may also benefit from a wrist brace that includes the thumb.

Cehck activities: Do an activity checklist. Try to remember if you did anything strenuous prior to the symptoms developing. Also, do you do repetitive work or leiiure activities? Do you have symptoms in other parts of the body such as pain and stiffness in the neck and arm? Do you have symptoms like this before. After activities, acute or chronic in your muscles have the symptoms be checked by a family dr.