Swollen joints can be a very painful and annoying condition. Overall there are many possible causes of swollen joints, and this is why it is best to see a physician who can do a complete history and physical exam to help determine what might be causing this complaint.
Swelling in the lower extremities can be caused by cardiac conditions, including heart failure. This would be an unusual presentation in a patient in his or her 30's, but there are things such as viral infections or previously unknown valve abnormalities that could cause cardiac problems leading to swelling in the ankles and legs in a young patient.
Rheumatologic diseases can also cause joint swelling, and these conditions are often diagnosed in young patients, especially women. The pattern of joint swelling, other associated symptoms such as weight gain/loss or hair/skin changes, and family history can be an important part of a rheumatologic evaluation. Laboratory tests can also be performed if indicated by the history.
Kidney or liver disease can also cause swelling in the ankles. It would be unusual for either of these things to appear suddenly without any other symptoms, but a general history and exam can help determine whether any basic laboratory testing should be done to evaluate kidney and liver function.
Overall there are many things that can lead to ankle swelling in a young adult and the best way to determine what is going on is to see a primary care physician
who can do a history and exam and then refer to specialists if needed.