My neutered 15 year old male cat started to be sick last week. He was not eating or drinking. I took him to the vet who did blood work and x-rays. The x-rays show no blockages. The blood work shows very slight beginning of kidney disease. The vet gave him a saline (hydration) shot that absorbs within 48 hours, antibiotic, anti nausea meds. He is drinking more now but not eating. Any ideas of what is going on with him?