Have Stomach Discomfort, Nausea, Dizziness, Loose Stools. Ideas?

Hi,
I have been experiencing strange symptoms lately that make me think of myself as a hypochondriac, only I am genuinely experiencing these symptoms.

I am a 22 year old 5'1", 106 lb female who, after eating certain foods, gets a feeling in my stomach resembling the feeling I get on my teeth after whitening them too often. It is a hollow, cold feeling providing me with just enough nausea to ruin the part of my day for which it is present. I have associated symptoms of occasional, slight dizziness and have the occasional loose stool but not too bad.

I am generally a healthy person, doing hot-yoga regularly, and keeping red meats out of my diet.

I have contemplated things that it could be such as an allergy to onions... However i have recently noticed that upon eating Multi grain Cheerios, I am once again reunite with this discomfort (I am lactose intolerant so I use lactose free milk-- rule out milk)

I really just wish I had SOME idea of what this could be.. I am beyond exhausted of it and the associated harping about it to my darling.
Please help me.