my baby is eating a ton of formula!

He's almost 4 months old, he'll be 4 months may 10th and is taking 6 oz every 2 hours. And even started giving him 8 oz every 2-3 hrs. So the doctor said to try some rice cereal, he hates it, I don't force it or anything, i try. And he spits it out and i just give him the bottle, is there anyone that can give me som advice? Am i doing something wrong or does my baby just not like it? Lol FTM.