Background, my 3rd child is currently 14 weeks, he is exclusively breastfed.
He weighed 7lb 9oz at birth, 5 days overdue.
At 5 days he weighed 7lb 11oz, at 2 weeks 8lb 3oz, at 8 weeks 10lb 11oz.
So in the first 8 weeks his weight gain averaged 6.25oz.
At 14 weeks he now weighs 12lb, average weight gain for last 6 weeks 3.5oz. He has dropped from 50th centile at birth to 9th at 14 weeks.
He has slept 11/12 hours at night without waking to feed since 7 weeks.
In the day he feeds a lot, and certainly lets me know when he is hungry!
The HV wants me to go back next week to have him weighed again.
Now my 2 DDs followed exactly the same pattern, they were both EBF and at 14 weeks weight gain had slowed down, and both had lost weight by 16 weeks. DD1 the doctor told me to give her 1 bottle of formula a day which I did, but then weaned her about 2 weeks later, she put weight on again very quickly. When I saw the same doctor with DD2 he told me to wean her, as clearly my children did this. She also put on weight again very quickly.
I will go back next week and get him weighed again. But if he hasn't put any weight on, or very little, or lost weight i am against giving him formula for a few weeks when actually with DD2 from just weaning her at 16 weeks she put on 18oz in 2 weeks, went back up to the next centile line and has stayed there ever since.
Ironically when I took him to be weighed this week and the HV said do you have any concerns, I told her about my DDs while I was undressing him and she said oh he looks very healthy, he is very alert etc etc, let's just wait and see when I weigh him, I am sure he is fine. (As if I was being overly concerned or something). Then once she weighed him she wanted me back next week!