White spots on teeth?

I've had white spots on my two front teeth for as long as I can remember. I'm almost eighteen, if it helps. I've heard of a few different reasons why they're there. I believe mine is from the calcium deficiency, but I'm not quite sure. My mother also has them, but in honesty I really used to not take care of my teeth at all for a couple years. The spots haven't really bothered me too much, mostly because my teeth are already pretty crooked and two white spots are nothing compared to how my teeth look. But, after using a sample of the Crest White strips Advanced, I noticed they look a great deal brighter compared to the rest of my tooth. I've used the Crest White Strips Premium, and it didn't happen that time, so i'm wondering why the spots are even brighter. Is there a way (aside from the expensive veneers, I dont have great dental insurance) that I can lessen the brightness of these white spots? I'm now afraid to use more whitener, in case it could brighten the spots even worse than they are now.
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They could be from too much Fluoride, or they are there from a medication you may have had as a child when the teeth were developing. Whitening will continue to make them stand out more I'm afraid. Have you had braces? Sometimes the glue from the brackets can remain on the surface of the teeth. Pop in for a check so the dentist can see what it is and tell you what you can do.
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