How old was your child when you started adding cereal to their bottle? My son is always hungry!?

My son is 7 weeks old, and is eating 5 1/2-6 1/2 oz every 2-4 hours, he seems to be always hungry. Trust me, I'm not force feeding this child, when he's done he spits the bottle out, for a couple weeks he was actually sleeping through the night (8 hours) after eating a 6 1/2 oz bottle, now he's waking up every 3-4 because he's hungry. I know it's because he's hungry by the way he sucks the pacifier if I try to sooth him back to sleep. It seems like he's eating an awful lot, I've heard that putting rice cereal into their bottle before bed time helps them sleep longer because they stay full. So my question is when did you start introducing cereal into your children's bottles? I don't want any negative effects from doing this if it's too early, but I also want my child to be happy!