Achilles Brace causing pain??

18, f, 5'9, 116lbs. I overused my achilles by walking too much (I have other problems with my ankles and legs that make this very easy to do) and a doctor here in France gave me an achilles-specific ankle support brace. I put it on and it is very snug - practically skintight - and at first is comfortable and relieves the pain, but soon starts to hurt my achilles more than when i dont wear it.

What the heck?? Don't know what I should do. It's really hard to get off of my leg. It might also be irritating my ankle because they pronate too much, so maybe the brace can't get into the right position because of my ankle movement. Dunno. Frustrated, any advice would help!