Why am I getting white hair at the age of 18?

I first started noticing them when I was 17, a senior in high school. They seem to be increasing in number...I pull them out all the time and I usually get about twenty or so every month. That's just the observable ones; I'm sure there are others (less noticeable, in the process of changing color, or too short to pull out) that I haven't reached so that the actual number is probably closer to 40~50. Why am I getting so much white hair? They're not gray or even regular white either; they're silvery and shimmer in the light. Once in a while I also notice that it's actually pale blonde instead of silver (really weird considering I'm asian). My mom thinks its stress + lack of sleep. I think it's probably those factors, plus some vitamin/mineral deficiency or other lifestyle problem that I'm not aware of. Any ideas?!