Add insult to injury. Throw salt on a wound. When it rains it pours.
Yesterday I discovered a neat way to say this in Japanese:
naki tsura ni hachi
lit. crying face bee
A bee stings an already tear-stained face.
Use this when on top of misfortune even worse things happen. I imagine if Charlie Brown spoke Japanese, he’d turn this perfectly good kotowaza into a cliche.
The Kenkyusha J-E gives a couple of examples:
nakitsura ni hachi de
to make matters worse. On top of all that…
nakitsura ni hachi to iu wake sa.
One misfortune led to another.
The というわけさ is という like this わけ meaning/reason さ ending indicating assertion that this is so.