FIP Diagnosis

People who’ve had experience with getting a diagnosis for FIP, what were the steps on giving a fairly clear diagnosis? We have done blood work (FIP Profile), testing the liquid in her belly, and an xray. We will possibly be doing an ultrasound today. My frustration has been al the doctors saying it might be FIP, but can’t say it’s definitive so it feels like they are waiting until my baby gets worse. Overall, her mood is good, she just has the bloating in the stomach and mild diarrhea. It’s been about 3 weeks since I have noticed her stomach getting bigger so I feel like I’m running out of time. Anything helps!