But the sooner you find out, the better off you'll be. Eating food that you're allergic to is the same as getting food poisoning, so it can end up ruining your liver and kidneys. It's not easy figuring out what you're allergic to on your own because you may not get the headache until three days after you eat it. For me I started getting the runs within half an hour after eating tomato so I had a way of linking the two together. It wasn't until I quit eating tomato completely that I realized that I was no longer getting headaches. When I asked my doctor if there was anything I could take for it, he told me to look at all the side effects listed on some of those allergy relief medications they advertise on TV. Those side effects are nothing in comparison to the side effects for tomato allergy medication. My sister went to an allergy specialist where they placed a bunch of different patches up and down her back to test what she could be allergic to. They ended up finding a number of different things. There was no way she could have figured it out on her own because if she quit eating one of them, she would still get sick from one of the others. Over the years it's gotten a lot worse, I can't even eat KFC or Nacho Cheese Doritos because they contain tomato powder. Last time I ate a piece of KFC it felt like I had a sinus headache where my head was gonna explode for an entire week, but at least it wasn't a migraine.