Hi I'm not surprised that you're stressed.
I was diagnosed at the age of 19. I too was slim, and apart from the thirst and frequent urination, tirednessI felt quite well. At the time of my diagnosis I had what I thought was flu for 2 days. My blood sugar was only 17 when I was diagnosed. I'm quite sure things came to a head because I had a craving for sweet things and constantly stuffed my face with cakes and sugary drinks. The doctors were in no doubt that I was type-1 and I was put on insulin straight away.
Type-1 is an automimune condition- your body no longer produces insulin, although up to a year after diagnosis you can experience a "honeymoon period" when your need for injected insulin drops drastically, if not altogether. However this doesn't last,and does not mean your diabetes has gone. You will need more insulin again and for life.
Type-2 as far as I am aware occurs when the body becomes resistant to the insulin it produces, and oral medication helps the insulin work effectively. It is more common in older overweight people.
As for type-1.5, I am dubious about it's existance. Prob the invention of a confused GP.
I hope your specialist can advise you better, but I think you are type-1.
Let us know how you get on at the hospital and good luck.
Jus