I fed ds1 until he was 2. He literally self-weaned the week of his second birthday (I was pregnant again and I think the milk dried up).
It was an enormous feat to get to that, I had horrendous early problems and before 6 months he actually failed to thrive, going from the 75th to 0.4 of a centile and I had to supplement etc. It was a gradual rather than a sudden decline and I had all sorts of intervention from the local health services. For weeks, I fed two hourly for 45 minutes and then expressed and refed. Breastfeeding was a battle for much of the first four months, and looking back, he was a miserable scrawny angry baby who just needed more food. I became really obsessive about nappy counts and his weight, and this gradually tipped over into full blown OCD (though I didn't realise it back then).
On good days, I tried to cod myself that he was just meant to be thin and his birthweight had been inflated blah blah blah but when he bounced from 0.4 to 50th centile within a month of starting solids, it was pretty clear he hadn't been getting enough milk. I still feel really guilty about that.
Ds2 is 5 weeks. He was 9lbs 3oz at birth but within three days he had lost a pound. I totally freaked out between the day 3 and 5 weigh in and shut myself away in my room having panic attacks about it and barely fed him I was so strung out 
. I am being seen by the perinatal mental health team locally for my OCD (which reoccurred in my pregnancy this time) and they sorted out that he wouldn't be weighed again for at least a month and the support I would get would be based on looking at him vs the scales.
Anyway, today was his first weigh in since day 3 when he was 8lbs 4. He is 9lbs 9 now, so he has gained about 4.6oz a week and dropped to between the 50th and the 25th centile (infant growth chart says 39th). He's not really gaining as I want him to be and I am in a total quandary.
I don't know what to do. I know objectively that he is a happy feeder compared to his older brother - he feeds well without me having to work hard at it, I can hear him gulping down milk, he is calm and happy between and during feeds, he is cooing, he is smiling, he pulls off the breast himself and seems satisfied, he wakes to feed. His wee output is immense, every single nappy weighs a ton... his poo is the right colour but it is very variable as to what he will do, he did 4 nappies yesterday and so far today there has been none despite him having lots and lots of feeds.
He is not amazing at taking a lot of breast into his mouth and I have to work at his latch a bit. I can do this and know all the tricks to get him deep onto the breast, but he will tend to pull back off onto the nipple midfeed. This is not a problem when it is just us two but I guess when his older brother is around (2.5) sometimes I let it go more than I would because I am distracted by trying to prevent him from being squished or having stuff thrown at him.
I know I can't go back to the punishing schedule of expressing after feeds. I allow him as much access to the breast as he wants, we do lots of skin to skin and biological nurturing on the three days we are here alone (ds1 in nursery). I never cut his feeds short on these days, I work to keep his latch good etc. It's just not working the way I had hoped.
I want to breastfeed him but I am not prepared to take crazy measures this time, nor am I prepared to just keep going if his weight starts to drop through the centiles, which I am guessing it might if he's gaining less than he should on average. What should I do? Should I supplement? Should I wait until after the six week growth spurt to supplement? How much should I supplement, if I do?
Thanks for reading.