When dealing with any pain or swelling in joints one important question is to determine whether the swelling and pain occurs more toward the end of the day or more toward the beginning. In your case it sounds like you feel fine in the mornings and are in pain at night. In many ways this is good news, because more serious causes of joint inflammation, like rheumatoid arthritis
, tend to cause stiffness in the mornings that gets better over the day.
That being said, you should have the ankle checked out by your primary care doctor
, because several months of pain and swelling is too long without having a medical exam.
One possibility would be that you have a bursitis (inflammation of the joint capsule) which can wax and wane but is generally a benign condition. Another would be that the swelling is more from dilated veins in the legs that don't work so well at returning blood to the heart (varicose veins
), although this usually occurs in both feet at the same time. With any one-sided swelling it is important to make sure there is no blood clot, although it sounds like not given the fact that things are better in the morning.
Regardless, the first step is to see your primary care doctor.