Feeding 3 month old baby oatmeal

So my son does not sleep at night like at all!! A coworker told me to try and give him oatmeal with his formula before bed and it should fill him up. She’s a nurse we both work in the medical field. My son will be 4 months in 2 weeks, is it too soon to try it out?? Also is it too early to try baby food like banana?? I feel like he’s so bored of his formula.