Chemotherapy causes nausea and vomiting as a side effect by destroying the lining of the digestive system. This lining regenerates after the chemotherapy is stopped but during it , these side effects are common. You need to do 2 things. First take anti-vomiting drug (Tab Ondansitron 8mg thrice daily or SOS) and maintain a sufficient diet to allow regeneration of the lining. Since his appetite will be down, try finding foods that he tolerates or likes and increase their amount and supplement them with vitamins and protein powders. He will like sour foods better than sweet or salty. As to the back pain, it can only be decreased by taking pain kilers. Tab Paracetamol 1g thrice daily should suffice.