The bone that protrudes from the inside of my left foot, right above the arch, is extremely painful to the touch and swollen. what could this be?

Protrude=wrong: Nothing should really protrude, so should be seen by urgent care dr or podiatrist for exam and diagnosis.

Many possibilities: Pain in that area could be due to trauma (fracture, tendon or ligamentous tear, arthritis), infection, metabolic conditions (gout) musculoskeletal (bony over growth) or biomechanical abnormality, or neurologic conditions (neuropathy). A thorough history and physical exam and possibly laboratory and radiology exams could determine the cause. Have it evaluated by a professional.