Long story short, none of my babies gained weight on my milk.
The long version (copied and pasted from another post of mine - hope that is OK):
I struggled to breast feed my three sons. The first had neonatal jaundice and I was told I had to supplement breast feeds with formula. In hindsight, this may have been bad advice, but at the time, with my newborn son in an incubator, under UV lights, I did what the medical professionals told me.
When we were discharged, I tried to reestablish exclusive breastfeeding - I even used a hospital grade breast pump to try to boost my supply, and it had no effect whatsoever. I ended up having to formula feed No1 son, and felt like a failure.
With No2 son, I was determined not to 'fail' again. He was born at home, and lost 10oz from his birthweight. The Health visitor was very concerned about this, and the fact that his weight gain was very, very slow. She was visiting daily or every other day, and insisting she wanted to see a 0.5oz weight gain every day - and this just wasn't happening.
At 6 weeks old, he developed a chest infection and was admitted to hospital. The medical staff were not particularly concerned about his chest, but were very worried about his lack of weight gain. They used the terrifying phrase 'Failure to Thrive'.
I was told he was being kept in until he started to gain weight at a good enough rate - and this did not happen until I introduced formula top ups - which spelled finis to breastfeeding - but I felt I had no choice.
With No3 son, I mixed fed almost from the start - breast during the day then one formula feed late in the evening and one during the night. If I dropped even one of these formula feeds, his weight gain stalled.