British Shorthair Cat not feeling well...?

My cat Gracie is 5 years old. She was bottle fed by the breeder due to the mothers milk drying up so she has always been kind of susceptible to illness. She has developed allergies which we get steroid shots for every season, but this year she started hacking, almost between a purr and a hairball but more upper lung area and more fluid like. When I took her to her vet she had a temp which we started amoxy drops for, we couldn't do bloodwork because of the temp and possible infection. We thought upper resp infection at first but I have 6 other cats who have shown no symptoms and Gracies congestion is no better. She doesn't feel well I can tell but she is eating and grooming herself. She has had some gradual weight loss which concerns me because of everything else that is going on. So my question is, has anyone else had a cat w/ these symptoms and if so what was the diagnosis? She goes back to the vet Monday for bloodwork.