Usually if you have responded to an initial injection, then you will respond in a similar manner to subsequent injections. If you have had no relief in your symptoms but the muscles are relaxed by the injection, then other treatments may be required.
It may be that due to development of new problems (such as endometriosis or other pelvic problems) that the injections are not as effective as previously. If this is the case, then it may be suggested that further investigations or tests are performed.