Quote Originally Posted by Wahine View Post
Going to the doc sounds like a good idea and then you'll likely get sent to PT. The area of the ankle you're talking about is where some tendons run (not the achilles) so you could have tendonitis there. These get inflammed sometimes when a little ligament that holds them in place gets over stretched. But the time when you have pain (hills and down stairs) is often related to the calf or achilles. The moral of the story is that it doesn't fit into a nice clean diagnostic picture so it's best to get it checked out live and in person.
These are the peroneal tendons. I've had peroneal tendonitis, and I had basically no swelling, even to the point where it hurt to walk. Instead, the tendons just protruded out below the ankle bone, because they were so tight. I also felt the most pain at the attachment point in the foot. It was sore behind the ankle, but nothing significant, and only when the physical therapist manipulated them deeply.

Extreme swelling is a huge red flag. That wouldn't be something like tendonitis but a rupture or a sprain involving ligaments. Go to a doctor and get it examined asap. Ice regularly and elevate it in the meantime.