I have pain in my outside ankle the pain comes and goes there is a little swelling. what could that be?

Many causes: There are plenty of causes of foot/ankle swelling. First, you need to make sure that you are not in acute pain, which could indicate a blood clot. An ankle sprain may also cause pain. Added salts in foods, lack of calf strength when walking, diabetes, etc. Make an appointment with your local podiatrist who can better differentiate the swelling and recommend a plan for you.

Strain,Sprain: Stress fracture, and soft tissue tears are some causes. I suggest you be evaluated before it gets worse.