Hi Laura,
Gluteus Medius is a stability muscle rather than a power muscle. I would be wary of the fact that you have torn it. When this happened did you have any bruising?
Firstly I would go to the physio. I would get thesacroiliac joint checked out as well as the hip. The sacroiliac joint is affected by impact activities e.g.running, and when it becomes inflamed the gluteal muscles tighten up as a protective measure.
I wouldn't advise running at the moment, but non-impact activities should be no problem.
I also agree with Yarok, in that it would be interesting to check if your past achilles injuries are linked in any way to this.