respiratory / lung infection

My mother in law has been sick with a respiratory infection since mid April. She was admitted to hospital for 3 weeks, where they were treating her for pnemonia (pneumonia). As it turns out they dont think it was pnemonia (pneumonia), cause all the different antiobotics they were giving her did NOTHING, no one bit of difference to the infection in her lungs.

She had x-rays and scans every 2-3 days with no change in her condition. They then took her for a biopsy of the infection in her lungs, and still they dont know what the infection is ??

She has now seen another doctor, who has prescribed cortisone tablets, there has been a slight improvement in her xray and she has been on the tablets for 3 weeks now.

I just wanted to know if anyone has any ideas or would know of any other treatment.

She is run down, tired all the time, cough a little bit, has pain in the chest/ribs, she doesnt have any phlem coming up at all.

thanks