Albeit very slowly.
He was born on the 50th centile, 7lb 15. We went onto weighting him monthly after about 7 weeks. He stayed pretty much on the 50th for the first few weeks and has very gradually been dropping since about 11/12 weeks (obviously, since he's weighed every 4 weeks or so, it's not an exact science!
). At his 16 week weigh-in he had dropped to the 25th centile and today, five weeks later at 21 weeks, he's 14lb 11, halfway between the 25th and 9th centiles. He's put on 15 oz in the last 5 weeks.
Is this gradual dropping a natural thing or could it have something to do with the way he feeds at night? We cosleep, for my sanity mostly, and though he might wake as often as four times between 10-11pm and 7am, he nuzzles close, has a very quick suck and is back to sleep - never really wakes properly. Whereas if he were in a cot beside me, he'd wake properly, cry etc and probably (remembering how it was with DS1) have a good feed before being put down again. I'm wondering if this might explain his slowing weight gain. He's still little, so he does need a decent night feed! 
HV was a bit more concerned this time than last month, and when I suggested this theory she thought I should really try to get one good nightfeed into him. I'm steeling myself to try this (the reason I cosleep is in order to get a decent night's sleep!) but does any of this sound at all alarming?
DS2 is generally active, not sitting up yet but trying hard to
, loves people and watching his older brother - in other words, normal and healthy. BUT he can also be a very grumpy little customer and isn't what I'd call 'placid'. He fusses and complains a lot more than DS1 did and isn't as avid a bf-er as he was. So of course, though I should know better, I'm now getting a niggling little voice saying 'Maybe that's why he cries a lot and isn't always that happy. He's hungry and not getting enough milk'.
I feed him on demand, but like I say, he isn't as enthusiastic as his brother was - but presumably if he was hungry, he'd stay on longer? 