If you are having a hard time beating scabies you should check this article out, it could be that you have a more advance stage of scabies called norwegian scabies which in its worst stage starts crusting the skin, and some times you have to treat naturally as some scabies have evolved and are resistant to the permethrin treatments.

source: Norwegian Scabies vs Scabies

http://www.goarticles.com/cgi-bin/showa.cgi?C=2337380

Some scabies probably need different treatments as some are resisitant in certain conditions, I would look at using natural treatments at first and use chemicals and pesticides on your body last if everything fails. There are even reports that permethrin creams are not working on scabies and that the natural products are more effective and actually help your skin more instead of harm it. Scabies can be a tough condition to cure, especially when some have problems telling if they have scabies or post scabies.