Non-Hodgkin B-cell Follicular Lymphoma, Rituxan Cough, Sinusitis, Osteomyelitis, Mastoiditis. Done Chemotherapy. Why Joint Pain?

Is it common for a person to have more than 4 rare or "uncommon" diseases at one time? After my 60 year old husband went through Chemotherapy for Stage 4 Non-Hodgkin B-cell Folicular Lymphoma (which is in supposedly in remission) he developed several "life threatening" rare diseases. I am not convinced the cancer is in remission or if there is a bigger picture to all of these diseases he developed. He was healthy up until they found the cancer 3 years ago. He had developed, after his 2nd chemo maintenance treatment, a severe cough that was ruled out as Pheumonia. They called it "Rituxan Cough" caused by the chemo medication. After that within the last 2 years he has been hospitalized about 6 times and developed: 1) Sinusitis 2) Skull Based Osteomeyitis 3) Mastoiditis in both ears 4) Significant hearing loss in both ears 5) Achromobacter Xylosoxidans discovered from an ear culture 6) Low IGG levels 7) Mycoplasma Pneumoniae found in a DNA test from the bone tissue during a mastoidectomy 8) Bronchiolitis Obliterans with Organizing Pneumonia (BOOP). He also has undiagnosed numb toes and joint pain that comes and goes and now he has been having dry heaves every day for the last month with loss of appetite, weight loss, feeling full after 1 bite, night sweats and intermittent feavers. He has been on and off Prednizone and Antibiotics (about 10 different kinds oral and intervenious) for the last 2 years. Every doctor he sees says he is a difficult case and don't have any answers. Any suggestions?