Is it possible that I have dementia at 17 years old?

I wikipedia'd it and the symptoms seem to apply to me fully. I've had insomnia since I think 14 years old (see I can't even remember when) to about 16 years old, which I think was caused by ginseng tea because I drank it almost everyday (I've stopped now). Now I sleep fine, but I think those 2 years of insomnia did something to my brain. A year ago I was extremely disoriented in time; not knowing what day it was, what month it was, even what year it was. When I wrote the date on my pages at school I would write 2010 instead of 2009. Now it's not so bad, but my memory is still bad and bothering me. A year ago my memory was so bad that when I read a sentence or heard someone say something I would forget literally instantaneously after. I have very, very few childhood memories. Today my memory is not as bad, but still very bad. So, do I have dementia??