Still not sleeping well at 4 months

Tiffany • Abby came early emergency c-section. 3/3/17💕 Mommy & daddy are so in love! RIP to my fiancé. 5/21/17 gone way too soon

Ok my daughter still wakes up like every 3-4 hours to feed during the night. Her dr said to give her rice cereal but I think she is having an allergic reaction to it so I want to stop it for a few days. What can I do for her to sleep longer and me?