Dog is sick, dont know what to do?

im 17, and well my dog is basically my best friend, shes only 5 and about a month ago she lost her appetite and stuff. We took her into the vet and did blood tests, and they gave us something for her liver, however that isnt the problem because she didnt get any better. since that we havent taken her back to the vet due to the fact my mom cant afford an ultra sound or x rays. my dad is rich and i asked him for a loan, and he said he didnt think it was money well spent. Ive literally tried everything, She eats ok some days, and bad others, and she is lethargic. what breaks my heart is the fact that she is so young, and could die, shes a smaller dog so she should live atleast into her teens if not alot longer. I pray multiple times a day for her, hoping she can get better.... I dont understand how I am so attached to a dog, i mean I have had a couple dogs who have passed, which sucked, but I feel like I would be destroyed if this dog were to pass away. what do you suggest I do?