Suggest Treatment For Pain In Buttock Due To Repeated Injections

Hi I had an injection of 200 mg of antipsychotic in the right buttock in April 2010 and at the time it really hurt. Since then I have had pain there. When I am injected on that side it intensifies the pain. I am forced to have the injections in the left buttock all the time now and walking is becoming difficult. What do you advise please? The injections are every 2 weeks of Glucopenthixol.