Hi, I'm 16, 6'2 and 188lbs.

I have been overweight since i was around 12 years old. Like a year and a half ago I weighed 225lbs and I went on a "calorie cutting" diet. I reduced my calories to only 1400/day and I lost the weight fast and got down to like 185 in 8 months. I then quit the diet. Its been almost a year since I quit off it and I noticed I was gaining weight again and I had never really gotten down as much as I wanted to anyway. So two weeks ago I weiged about 200 and decided to lose weight again. Only this time I'm exercising a lot more. So I cut the calories to 1400, even off my diet I never ate more than 2200 a day.

Today i get on the scale and I only weigh 188, thats 12lbs in 2 weeks. This scares me because I know your not supposed to lost more than 2lbs a week. So is this really like fat thats burned off or water or muscle or what that I lost? For exercise I strength train, use my bike, or play tennis almost everyday. Why has the weight dropped so dramatically already. And advice?

i wouldn't be too worried unless this goes on for a longer amount of time.

It's sorta expected the first week to three weeks or so, you're not really losing weight. you're losing SOME weight but alot can be just water weight as well.
from personal experience, I once lost 8 pounds in one week.

so like I said, as long as you're eating healthy and you don't feel sick, you should be okay. if you find that your weight is dropping very quickly even after the first month and you don't know why (ie: you're still eating fairly and exercising moderately), go see a doctor to make sure everything is okay... like you aren't overexerting yourself or eating improperly.

the other bad side to losing weight so quickly is that your skin can't adjust and "bounce back."

if EVERYTHING seems to be okay... other than what I've mentioned... I suggest you buy a new scale.
and if you're still finding you're losing alot of weight, then pat yourself for a job well-done.