Does my cat have feline leukemia?? Or something else?

My vet did a feline leukemia test on my cat and it barely showed up, so slight it was hard to see. She has lost a lot of weight, but still eats. Her fur looks not as pretty also. But how do i know if she really has it or not. She has watery eyes also, and sneezes, i was given medicine to treat that, but it doesnt seem to go away. Other than that she seems really fine. Im really confused. If anyone knows more about this please help with some info. Im really confused! Thanks!!!