Step 4: Read and complete the decision guide to learn more about your symptoms.
From your answers (ankle pain for less than three weeks that is neither mild nor severe, without fever and without other joint pains, but with swelling and morning stiffness), a number of conditions come to mind.
A sprain or tendonitis could cause these symptoms.
Osteoarthritis could do this, especially if you are over the age of 50 or have had previous injuries to that ankle. Pain is usually worse with walking.
Ankle arthritis may accompany conditions causing arthritis in other parts of the body (such as rheumatoid arthritis) but there is usually pain in other joints; past psoriasis, diarrhea or a sexually transmitted disease may be of particular importance to you (see arthritis associated with inflammatory bowel disease, psoriatic arthritis or Reiter's syndrome). Joint infection (including Lyme disease) is a relatively rare cause of ankle pain such as yours.
There are other possibilities (if you can believe it!) and early treatment is important for many of these, so it is important that you see your doctor soon for evaluation.
If your ankle pain is already improving, you may just need to give it a bit more time; over-the-counter anti-inflammatory medicines (such as acetaminophen or ibuprofen) are reasonable to try unless you are already taking them or your doctor has told you to avoid these. If symptoms persist, see your doctor for evaluation.