Help, VERY SICK CAT

Help, VERY SICK CAT

My 18 year old cat began having difficulty keeping things down about 3 weeks ago. I bought her wheatgrass and it helped her bring up some huge hair balls. She continued to bring up her food. I took her to the vet Friday before last. He took bloodwork and x-rays. Heart is enlarged which is normal for a cat her age. All other organs are functioning good. Has no temperature. Gave her medication for intestinal gas possibly due to infection. Kept a little milk down and some tuna salad. Took her back last Tuesday for vet to trace berium through her system and take xrays. No blockage. Esphogas muscles are relaxed which is normal for cat her age. Told me to encourage her to eat soft foods. Three weeks ago she was eating 2-3 cans of Fancy Feast a day. She won't eat the perscription food which I mixed with other food like he told me. Milk seemed to hard to digest so I got her catmilk yesterday. She drank a little over 6 ounces with a little more tuna salad and seemed to be keeping it down. She wanted something else, so I drained the water off a can of tuna which she usually likes. She took two laps and brought up everything. She doesn't seem to be digesting it. I'll call the vet tomorrow, but can anyone suggest anything to try? This is hard on her and me. She is strictly an indoor cat and a 2 person cat. It causes her such trauma to take her to the vet especially since she has never been sick before this. She had a sinus infection several months ago which caused her to sneeze 15-16 times in a row and she wouldn't eat then. After taking her to the vet and giving her the antibiotic, she became fine again. Please pray for her and me.