G.B.
Well, since babies are not supposed to eat any food until they are at least 6 months old I would say he's not ready. That is what his body is telling you, please listen to your child. He is too young to eat food.
The food you are feeding him is taking up space that your child needs for his formula. He needs the nutrition of the formula. Rice cereal has no nutrients in it other than some fiber to make him feel fuller. He will be lacking nutrition because you are feeding him food.
When he's old enough he should start with rice cereal mixed with a bit of formula and it should be a very very runny consistency. The whole purpose of feeding a baby food is to teach them to chew and swallow. They can learn that in a couple of months so they don't really even need food of any kind until they are even closer to one year of age.
Of course you can choose to do what you want but the state health department and the federal government won't even allow babies to start cereal or any other foods or drinks until they are at least 6 months. That's for WIC anyway. Our pediatrician thought that was nuts and that I had to be wrong. He said that babies should not start any foods until at least 9 months of age.