My dd2 hit her 4mth sleep regression/growth spurt quite hard. She went from 1-2 overnight feeds to 4-6.
The GP recommended solids to fill her up but my bubba isn't ready yet for that as she still can't sit upright herself.
But now after marathon bf sessions my supply has caught up and we've had a week of normal sleeps and I can finally celebrate... Till the next regression!
So for all those mums in the middle of the 4-5mth doldrums... It does pass, you just have to ride it out.