Boost stamina!

Hi!

My sister just gave birth! A healthy baby boy The problem is, there's not enough milk coming out and she claims to get tired easily every time she's breast feeding her baby, though the baby takes a formula milk we want him to be breast fed rather than taking formula milk, My aunt gave her vegetable leaf (IDK what that is) it helps her lactate and milk is no longer a problem though she still get tired easily, she eats healthy food though I think the reason why is because of during her pregnancy her Doctor advised her to be on bed rest I believe for 5-6 Months (not sure) and because of that she gained weight without exercise which she often do before she got pregnant, now I want to help her but I don't know any medicine or treatment that can help her boost her stamina, Plus we can't give her any medicine as it might also affect the baby.Hoping for any advise

Thanks!