Why is it that I feel physically ill whenever I eat junk food?

Just the other day our teacher bought us some candy for the last day of school, I had about 10 chocolate pretzels and I felt physically sick to my stomach. If I eat fast food I feel ill and I get a headache, if I eat candy from 7/11 my mouth feels horrible and I get a headache. Is it because I normally eat so... show more Just the other day our teacher bought us some candy for the last day of school, I had about 10 chocolate pretzels and I felt physically sick to my stomach. If I eat fast food I feel ill and I get a headache, if I eat candy from 7/11 my mouth feels horrible and I get a headache.

Is it because I normally eat so healthy and don't include any of this stuff in my diet? I drink a can of pop maybe once every 2 weeks. I eat candy even less. I also exercise a lot and I'm in good shape.
Update: Thanks for the answer titanook, I figured that.
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