My gp diagnosed me with scabies and prescribed lindane lotion I followed the directions for use of lindane lotion but it is 3 weeks later and I am still itching in places. How long will this go on?

Perhaps. Perhaps you should consider treatment with Permethrin cream. That is the standard cream used by most dermatologists. Do you have lesions similar to what you see on the link below? If so, you might still have scabies. I hope that helps.
As. As I answered in your other question about this, it sounds like your scabies might not have resolved. You should call you doctor.