Definitely see a doctor. I do have to say, though, that you seem to be describing very typical OCD symptoms, minus perhaps the fainting light-headedness, as OCD usually doesn't have such strong physical affects...though could be a consequence of diet, as gimmeice suggested. I do remember my chips and Coke teenage years, and it catches up to you now and then.

But back to the OCD...something can trigger you and suddenly it becomes your new pet obsession. For example, several years back I remember looking at a 10-dollar bill I had in my wallet, and noticing what poor condition it was in. Then suddenly I had thoughts that it might be counterfeit, or that a store clerk might think it was counterfeit, causing me to be arrested, thrown in jail, etc...doesn't make much sense, but these things never do. But the thing is, since then I've had this obsession about have good-quality money. I'm trying to work on it, but I still get hugely nervous when I have to break a 20 and the clerk pulls out my change...there's that fear of the unknown, what bills I'm going to get.

All from that one thought that flashed through my head in a second. So yes, see a doctor, but be sure to emphasize this aspect of your symptoms. I wish I had such insight into my own symptoms when I was your age, by the way.