Hi, sorry to hear you're having a rough time. It's not easy, is it?
What, in an ideal world, would you like your doctor to tell you next week? This might help you see what you wish might have happened.
Stop, for a moment, and write the kindest letter to yourself about your situation?
(If you're feeling angry with yourself, try writing it as advice to someone who you are very fond of, but who needs a bit of care at the moment)
People put on weight for all sorts of reasons, so it's important to be kind and realistic, but, kind to yourself.
And, over the next wee while, you're going to meet lots of people of your age, and in your situation - some of whom will also be scared, but also lots of people who can support you, and in turn you will be able to share your experience and knowledge with them.
So, yes, have a bit of a freak out for a day or two - that's normal, we all do it. And then knuckle down, learn a bit about what's happened, and what's happening, and move forward at your own pace.
Good luck