It's the age for it. And they can certainly be feeling ill without too many visible signs - it's quite likely if everyone else was sick.
Hang in there
Self settling is one of those things that we tend to bang on about in the West, but it's actually not really normal for babies to sleep alone or unaided. they do all learn in time, when they're developmentally ready. it's quite normal and natural for them to need help to sleep in the early years. Just all different, that's all.