It's not generally normal for a muscle to get sore while healing... but the pain will come and go depending on the demand that you place on the muscle. The amount of pain will let you know if your damaging or if it's ok to do that level of activity.
Have you checked a picture of where the sartorius sits to see if it is the same part of the leg? also did you have a surgery to fix the avulsion? and what kind of activity are you currently doing?