S.B.
I had the same problem with my little girl. Instead of rice cereal try using oatmeal with her formula. Oatmeal is a fiber and may help get things moving. Also another tried and true way is using dark karo syrup with water. My doctor suggested 1-2 teaspoons of dark karo syrup mixed with a couple ounces of water one to two times a day. Sometimes I would mix the karo syrup with her formula. I think it took about one day for it to really work and get her system cleaned out. Good luck.
S.