Dude, just had a quick lookover this thread - dont believe the scaremongering! Its human nature to think the worst. Everybody in my year (medics) has at one point thought they would die from cancer/rare infection/ congenital abnormality.
From what Ive read, its unlikely to be hyperthyroidism, you tend to have increased appetite, and other symptoms like irritabilty, fidgeting, sweating etc.
You're a young guy, type II diabetes isnt as common as type I. But you havent got any of the fairly serious symptoms that presents with (drinking and peeing loads, breathing faster). And note, in both conditions, you tend to feel pretty unwell, not just a bit lazy and tired.
But, as many have said, go see your Dr. Im sure they'll appreciate you coming down and sharing your worries.