Amanda, I'm so very sorry you're dealing with this. I'm sure it feels like you've been hit by a train-total broadside.
I was a care-giver for my mom, and I can only speak on my mom's experiences. She went from a negative biopsy by an ENT (for what ever reason, it was a false negative) of a horrible, painful, fast-growing ulcer on her tongue in September/October of 2014, to a "Stage T2" according to a second biopsy by an oral surgeon and a CT scan in early December, to thinking they'd gotten clear margins in early January 2015 after a hemiglossectomy and neck dissection, to being diagnosed with a very aggressive form of tongue cancer with spread to and out of a node and nerve invasion without clear margins by mid-January 2015 after the pathology report from her surgery came back. So she went from no cancer to early cancer to advanced cancer with removal and reconstruction of half her tongue and chemo and radiation in the span of about 4 months. The kind of cancer cells she had, along with the extension to and out of the nodes, made her disease more unpredictable than many.
What we all learned the hard way is that although we're dealing with science, diagnosis and treatment are not exact science. Even PET scans have to be interpreted and viewed along with biopsies and other information.
I do think there is an ugly side to cancer care, and health care in general, especially when you consider the high costs of cutting edge drugs and health insurance. But we knew the doctors my mom saw were almost as heartbroken as we were that her treatments didn't stop her disease.
I guess what I'm trying to say is that I understand feeling like the answer changes on you out of nowhere, but I'm so glad you're getting a other opinions even with the doubts you're experiencing. My hope for you is that you get a plan that you can believe in that includes the traditional gold standard treatments with doctors you feel a connection with. And if you want to investigate ways to supplement your treatment plan with some alternative approaches that help keep you strong, hydrated, nourished, and with pain under control, while you complete your treatments, that can only help.
I'm wishing you strength, sleep, and some peace of mind. I'll be thinking about you as you navigate things.