Feeding 4 month old questions

Li

Hey all. I’m a first time mom and my son will be 4 months on January 9th. He is breastfed/pumped bottles only. I understand that formula fed babies are fuller longer because it digests slower than breast milk. Right now my son eats ALL THE TIME! It’s Exhausting, he won’t sleep anymore because he’s hungry again by the time he falls asleep, and is up every 2 hours at night again because of this. I know he’s getting milk because he makes full diapers like clock work. On January 8th my family is moving from Maine to Arizona and we are driving.. 5 days in a car with a baby who eats every 90 minutes. I really do not want to give him formula. (Not because I’m against it, I just don’t want to unless I absolutely have to) am I wrong to consider adding a little rice cereal to his bottle a couple times a day?? I’ve talked to several other moms, but their babies were all formula fed so they were able to wait till 5-6 months old with no issues before starting cereals.. any moms out there who understand what I’m going through?? I’m pretty lost right now..