Any reason you started solids now instead of waiting until 6 months?
If you are going to start now, 2 tablespoons is a lot to start with. I'd start with a teaspoon to see how he reacts and work up from there.
BTW, what kind of cereal was it? Gerber cereal contains soy so you're better off with Beechnut or an organic brand like Earth's Best. But grains can be hard to digest - my own DD couldn't tolerate them until around 8 months.