I break out in hives after eating tomato sauce and running. What is causing this?

In the course of one month, I have broken out in hives 3 times! The first time, I had pizza and I went to the gym 2 hours later for a 20 minute run. After running, my body started feeling itchy and I noticed I was breaking out in hives all over. The second time, I had spaghetti and meat; again I went to the gym 2 hours after eating and the same thing happened. So I umed it was a certain brand of sauce. Yesterday, I went out and had pizza at a place that has been using the same recipes forever! I've eaten there a few times and never had any issues. It was raining really hard, so I decided to run back to my friend's office. I broke out in hives and well, it was a brisk run of maybe less than 10 minutes. It was not as long lasting as the other two. So, now I've identified the actions that cause my body to react, what is causing my body to react this way? What could it be?