Sounds like gas pains from eating more food and more fiber.
It happens to all of us at some point. Hell, I was doubled over last night with stomach pain from a huge plate of chicken stir fry. The frozen bag of veggies says it makes 19 servings, but I only get four. So I must get a huge amount of fiber in that meal...enough to give me some gas and gas pains.
What can you do? You have to eat big to grow.
Also, if you changed your diet from crap food to good food, your body will need time to adjust.
Amazing what shit food can do to you!!! It makes good food hurt! HA!