Yes, he could be allergic. My son was allergic to formula as well. We tried Similac. Once we switched him to NAN HA, he was ok. HA stands for Hypo-Allergenic. You can try NAN HA. If it still doesn't work, you could either try goat's milk or soy milk forumulae.
For the rice cereal, what brand are you using? Try not to use Nestle, as it has added milk contents as well as sugar and trace amounts of gluten. You can try Healthy Times, easily available at NTUC. Start off with single grain cereals.