I accidentally hit my ankle 3 days ago with a heavy metal lawn chair. (right under the ankle bone) there is no bruising and very little swelling. but to move it, touch it, put weight on it and walk on it, it is very painful. what could it be?

Need to examine: It is not feasible to provide a meaningful opinion without additional history, physical examination and may be some tests. It would be prudent to see your doctor, if it is not getting better and still have symptoms a week from now. You may take acetaminophen for the pain and use warm compresses. Wish you good health!

Uncertain: There is little fat or muscle protecting the ankle. When a object hits - it can sharply impact the bone. The periosteum is the outer layer of the bone and it is full of nerve fibers. Because of the nerve fibers anything that causes injury to the periosteum can cause a lot of pain - even if the overall injury isn't that serious. Take care.