1) "sleeping through the night" for an infant under a year is defined as 5 hours at a time. And many babies do not even do that until they are a year old-or more! Newborn sleep normally happens during the day as well. Just because a baby is not sleeping some huge amount at night does not mean baby is not sleeping enough.
And what a baby gets to eat often has nothing whatever to do with how long the baby sleeps. it is a myth that formula or bottles or baby cerial make babies sleep longer. Seriously it has been studied and there is no truth to this idea. Plus, even if it did make a baby sleep longer, it is so unheathy compared to breastmilk the trade of would not be worth it.
No matter how young you are or how planned or not the pregnancy was, you are your baby's mom, and you know your baby better than anyone else. All new moms & even experienced moms get a ton of unwanted advice, trust me.