EBF four month old is dropping on weight charts, poo changed color...

Erbear
So I've been a little freaked out since my son's four month appt were we learned he had been consistently dropping in the weight percentile. Hrs now in the 7th percentile, which isn't an issue, it's that he used to be in the 22nd and before that the 37th. I've had some great advice and encouragement from other moms here about that which has made me feel better. I'm curious if some of your breastfeeding pros can help me with another issue... He went from pooping once every 5-7 days from about 3 weeks until 16 weeks and now he's pooping with almost every feeding, which is great? I'm just curious about what prompted this change, unless it's just him being four months and growing up so fast. His poop is also more brown/yellow instead of yellow so I'm wondering what that means and if any of this had to do with his lazy weight gain?