I would definitely bring your concern up with the doctor. Don't wait for an appointment, just call and ask about it. I am surprised that the doc reccomended putting cereal in the bottle, since I have heard form various sources that doing so is a choking hazard. If your lo isn't having many wet diapers it may result in dehydration, which can happen really quickly with an infant.
So, I guess I don't have much advice other than call your doctor. And then, maybe call a different doctor and see if you get an alternative that you and your baby are more comfortable with.
“We are not put on earth for ourselves, but are placed here for each other. If you are there always for others, then in time of need, someone will be there for you.”