When my son was about two, I made the mistake of eating chili for dinner. I was breastfeeding, but nobody had ever told me to avoid spicy foods. Anyway, that night around 2 in the morning he woke up with projectile vomiting. We noticed because he was sharing our bed. Let me tell you, they call it projectile vomiting for a very good reason.
A week or two later, it happened again. We figured it out. No chili.
A couple of months later, I noticed that it took several extra hours to get him to bed on nights that I had chocolate chip cookies with my lunch.
Then, a chiropractor friend of mine suggested we take our son (and me, since I was still nursing) off dairy. Our pediatrician was getting ready to put tubes in our son's ears because of frequent ear infections. We stopped eating dairy and the ears cleared up, so the ear doctor decided not to do the operation. From then on, as long as we stayed away from dairy, no more ear infections.
As the years went by, we got in the habit of looking at food and what we were eating as possible culprits for all kinds of issues. With lots of experimenting, mostly trial and error, we found that fruit, of all things, made our son hyper. He could tolerate sugar pretty well, but one blueberry would have him bouncing off the walls.
When we went out to dinner, he would curl up into a ball on his chair after eating, until we stopped giving him soda with his meal as a treat.
His acne was so bad as a teenager, I was really worried he would scar for life. We tried topical treatments, but didn't want to medicate him, as he's so sensitive. Finally, we found the culprit - eggs! He stopped eating eggs, and all products that have eggs in them, and the acne cleared up.
I hear more and more about kids with sensitivities to foods. Adults too. When I changed my diet, I stopped having headaches, heart palpitations, constipation, itchy skin, sore throats... the list goes on and on. I hope that other parents will do as I did and look at what you're eating and feeding your family. Experiment with your diet. Pay attention to what you eat when problems arise. It just may be that it is your diet that is making you sick.