Firstly, try nto to worry, stress isn't helpful! (I know it's easier said than done but please try, you're doing your best what more can you do?).
To increase supply do as lulumama says, spend as much time skin-to-skin with baby as possible, bath together, and let her latch on at every possible opportunity, every suckle will stimulate your breasts, therefore make milk.
It is possible it could be a growth spurt, or baby could just be getting better at taking your milk, therefore feeding for shorter times, maybe making it seem they are coming off because there is no milk?
Is your DS starting to wean yet?
Or maybe DS has a touch of the bug you had and is feelign unwell?
Expressing is a really bad way to tell anythign about your milk supply, so please ignore it, you're best to just keep fedding, as often as possible.