I am summarizing this article about ankle sprains because it is technical and long, but it contains really good information. This should catch your attention, "More than half of people with a first-time ankle sprain will develop long-term residual symptoms after an ankle sprain and often develop a syndrome known as chronic ankle instability." MRIs and ultrasounds are not appropriate tests for ankle sprains because the injury is dynamic - the clinician needs to touch the area, checking for the location of the tenderness and the instability. If they do not do this, hobble to another facility. Also, it usually takes days for the initial swelling and pain to go down enough that a good physical exam can be done. Expect to be told to return after about 5 days. In fact, makes some sense to just wait 5 days, keeping your weight off the ankle, and if it still hurts after that, then go in. (If it stops hurting when you gently walk on it before 5 days is over, the sprain was mild and it will heal on its own).
Don't stress the ankle too soon - returning to sports, for example, can lead to chronic ankle problems. Hopping and dynamic balance tests are a good way to decide if an athlete is ready to return to play.
With a serious sprain (one in which ligaments are torn), avoid all weight-bearing for 10 days. After that, begin carefully controlled weight bearing. Don't use those boots for weeks and weeks - gentle weight-bearing helps the ligaments heal properly. Protected motion with taping and bracing are good choices from day 10 to 6 weeks after the injury. If you do not have a brace, google “taping ankles” and follow this pattern:
Rehabilitation to improve range of motion and balance is helpful after 6 weeks. Even the muscles surrounding the hip affect the stability of the ankle. Bracing should continue until all pain and instability is gone, and patients should be reminded that under the best of circumstances, the ligaments will not be at full strength for a year.
The full article: http://www.podiatrytoday.com/guide-conservative-care-ankle-sprains
In this case, Wiki has it mostly right, too: https://en.wikipedia.org/wiki/Sprained_ankle