fluctuations in milk supply?

Sindhu
Hello
The Last 3 days I've been struggling to make any milk cause lo is constantly hungry and he lost weight ..:: (and I can feel my breasts empty ) but today I am sooo engorged and just in one day LO gained 11 oz!!  Just feel like LO was starving the last few days and today he was overeatring  
He is one month and 3 days old. Is it supposed to be like this ??? Just feels weird and I haven't started pumping yet cause he won't take a bottle anyways.