unknown illness

unknown illness

Hello..i have a 7 yr old male tabby,he is a indoor cat and has been all of his life. He has always been healthy, good appetite..over the past month, we have noticed his coat was looking raggedy,he was loosing weight, and wasn't drinking much water.Now, over the past few days, he eats or drinks nothing,hides and never comes out,and walks with the hind legs wobbly. When he is picked up, he meows like he is in pain, like the hip is bothering him. He is very weak now, takes a few steps, wobbles, then lays down. He has been tested for Feline leukemia and tested negative. I have taken him to two vets over the past 4 days, they gave him a IV because he was severly dehydrated, and antibiotic ( for what I don't know) and we were sent home. I don't know what to do, I hate to see my cat, who is my best little friend, suffer. Any help would be appreciated.