Idioms for saying when one's bad situation compounded with more problems [duplicate]

A very common idiom is to say "when it rains, it pours."

"Pours" in this context means, "rains very heavily."

What this means, roughly speaking is "when one bad thing happens, you can expect a lot more bad things." So, for example, when talking to a friend who has just described a litany of bad luck in his life you'd say, "when it rains, it pours."

A fairly well known option is add insult to injury

to worsen an unfavourable situation

— wiktionary

An alternative is:

Out of the frying pan; into the fire

Which is usually meant as escaping a bad situation only to find oneself in a worse situation.

Two quotes from Shakespeare's Hamlet may be applicable:

"When sorrows come, they come not single spies/ But in battalions." --Act IV, Scene 4

"One woe doth tread upon another's heel,/ So fast they follow." --Act IV, Scene 7

Both convey the sense you're interested in, but the tone is academic/formal.