Completely new at this...

LO is 1 week old, he was 8 lbs 5 oz at birth, down to 7 lbs 6.5 oz four days later, a 12% drop in weight. The pediitrician stated that she didn't think my milk was in yet so she wasn't too concerned, but wanted us to offer 1-2 oz of formula every other feeding after nursing until my milk came in. She wanted him to come back two days later for a weight check. LO barely took an oz of formula at a time, but my milk came in later that evening. He nursed every 3 hours for 15-20 on one side and about 5-10 minutes on the other. When we took him in, he gained 5.5 oz in just two days. Our pediatrician was ecstatic, and said continue breast feeding and stop supplementing. She said keep an eye on his diapers and as long as he has enough wet/dirty everything is good to go. She said to let him go about 4 hours at night and let him nurse as often as he wants with no more than 3 hours between feeding during the day. He's been waking up at the 3.5 hour mark at night, and has been feeding about every 2 hours during the day. Still plenty of wet/dirty diapers but my concern is while his night feedings are still 15-20 minutes on one side and 5-10 on the other, his every 2 hours feedings are only about 10-15 minutes and he refuses the other side. The rational side of me thinks its normal, obviously less time between feedings he's probably not as hungry. But the hormonal and new mom side of me is freaking out that he's not getting enough. Is this all normal??
Sorry this is so long, I couldn't condense it any more. Thanks!