Sharing my experience, maybe will be useful. DS also gained not enough in his first week and I was really concerned about his weight - when he was born was somewhere between 2 & 10pc so not a big boy, first week only plus 110g.
What we did:
* Firstly I offered cluster feeding during evenings but I hated dramatic settling. Btw DF was also a normal waking for DS as when asleep he was not sucking.
* In first week I offered breast every 2,5h in he evening (not 2h as he was not hungry). So I feed him i.e.at 6:30pm, 9pm and 23:30. But as I said... it was dramatic.
* So in 2nd week I tried: no waking from 7pm to 7am - just feed when he wants, keep approx. 3h distance. In first days he was waking approx. when cluster feed before, but we needed couple more days and he settled his own routine. From 2nd-3rd week he was on 7x feeds a day, during nighs it was 7pm, 1am and 4am and then 7am. During days 3hŁ 7am, 10am, 1pm, 4pm and 7pm. I offered breast before and after bath so 7pm feed maybe calculated twice=).
* I offered both sides during all feeds and that made a change I guess! He was eating much more during day and from 2nd week he was gaining on weight more than 200gr-week.