Okay first cereal to early (and 3 months is to early) can cause allergies and tummy issues that will only make sleeping worse. Gas and constipation do not HELP a baby sleep. Second anything other than normal liquids in a bottle is a choking hazard, and it sounds like you are nursing anyways.
my son has never slept well. it's something with my kids, they don't sleep as babies, i think i'm cursed. But at 3 months my son still coslept and was eating every 3-4 hours, and only cat napping in the day. At a little over 4 months we finally fought and got him in a crib, but even at almost 10 months he's up 2 times a night, between 7 and 7, to eat. The only improvement is that he sleeps 2 hours in the early afternoon and takes a cat nap in the evening.
He will outgrow it, it will get better, you can not spoil him at this point and increase the amount of times he gets up. If he's just awake, by all means see if he can self soothe. This isn't CIO, this is common sense. There is a difference between a Cry/wail that means something is needed and a whine because he's awake. But if he's up and crying he needs you, even if it's simply because he needs a cuddle after waking up. You've been very lucky, appreciate it, and as hard as it is on no sleep, enjoy the extra snuggles.