My Cat is sooo sick, congested and runny eyes., HELP~~!?

I've asked this before...but I need more help. We adopted a cat from a shelter, he was sneezing the evening we brought him home. Took him to the vet and he has been on antibiodics three times, doesn't TOUCH his congestion. I've tried allergy medicine. I have heard it could be cat flu? Is that treatable. Don't bash us either, I take care of all my animals, I just don't see how taking him to a THIRD vet will help. Are there any home remedies, or has anyone else had this problem. He eats and drinks, normal stools, he limps ocionally and is ALWAYS snotty and stuffy......Help don't preach to me, please. THANKS!!