Yes its normal to go for days with no2's. As you have said you bub is happy, and contented, how he presents on a growth chart should merely be recorded for historical sake. Babies will grow at their own rates, they are genetically one of a kind and will do things their own way and in their own time. I am often amused by the obsessive need to fatten babies up so that they sit on a growth chart 'better'. If you bub is on the 25th percentile, all it means is that an average of 75% of babies are bigger than yours, not that he is underweight. You may find in the coming weeks he will have his 3 month growth spurt. BF bubs growth will usually fluctuate. You milk is the perfect concoction for your baby, there is no need to worry yourself with formula top ups, its just unnecessary calories. Trust your own instinct, sounds like you are doing great so far.