Dear Teresia, I have a few sutta quotes for you:
AN4.77:0.1: Numbered Discourses 4
AN4.77:0.2: 8. Guaranteed
AN4.77:0.3: 77. Unthinkable
AN4.77:1.1: “Mendicants, these four things are unthinkable. They should not be thought about, and anyone who tries to think about them will go mad or get frustrated.
AN4.77:1.2: What four?
AN4.77:1.3: The scope of the Buddhas …
AN4.77:1.5: The scope of one in absorption …
AN4.77:1.7: The results of deeds …
AN4.77:1.9: Speculation about the world …
AN4.77:1.11: These are the four unthinkable things. They should not be thought about, and anyone who tries to think about them will go mad or get frustrated.”
So there is no point in speculating about which deed could have led to which result exactly… unless you want to get crazy!
When the Buddha talks about kamma this is rather about what we can do now so it will lead us to a good path in the future, no matter what our situation is, like for example:
AN4.85:0.1: Numbered Discourses 4
AN4.85:0.2: 9. Confirmed
AN4.85:0.3: 85. From Darkness to Darkness
AN4.85:1.1: “Mendicants, these four people are found in the world.
AN4.85:1.2: What four?
AN4.85:1.3: ~The dark bound for darkness, ~the dark bound for light, ~the light bound for darkness, and ~the light bound for light.
AN4.85:2.1: And how is a person dark and bound for darkness?
AN4.85:2.2: It’s when someone is reborn in a low family—a family of outcastes, bamboo-workers, hunters, chariot-makers, or waste-collectors—poor, with little to eat or drink, where life is tough, and food and shelter are hard to find.
AN4.85:2.3: And they’re ugly, unsightly, deformed, chronically ill—one-eyed, crippled, lame, or half-paralyzed. They don’t get to have food, drink, clothes, and vehicles; garlands, fragrance, and makeup; or bed, house, and lighting.
AN4.85:2.4: And they do bad things by way of body, speech, and mind.
AN4.85:2.5: When their body breaks up, after death, they’re reborn in a place of loss, a bad place, the underworld, hell.
AN4.85:2.6: That’s how a person is dark and bound for darkness.
AN4.85:3.1: And how is a person dark and bound for light?
AN4.85:3.2: It’s when some person is reborn in a low family …
AN4.85:3.4: But they do good things by way of body, speech, and mind.
AN4.85:3.5: When their body breaks up, after death, they’re reborn in a good place, a heavenly realm.
AN4.85:3.6: That’s how a person is dark and bound for light.
AN4.85:4.1: And how is a person light and bound for darkness?
AN4.85:4.2: It’s when some person is reborn in an eminent family—a well-to-do family of aristocrats, brahmins, or householders—rich, affluent, and wealthy, with lots of gold and silver, lots of property and assets, and lots of money and grain.
AN4.85:4.3: And they’re attractive, good-looking, lovely, of surpassing beauty. They get to have food, drink, clothes, and vehicles; garlands, fragrance, and makeup; and bed, house, and lighting.
AN4.85:4.4: But they do bad things by way of body, speech, and mind.
AN4.85:4.5: When their body breaks up, after death, they’re reborn in a place of loss, a bad place, the underworld, hell.
AN4.85:4.6: That’s how a person is light and bound for darkness.
AN4.85:5.1: And how is a person light and bound for light?
AN4.85:5.2: It’s when some person is reborn in an eminent family …
AN4.85:5.4: And they do good things by way of body, speech, and mind.
AN4.85:5.5: When their body breaks up, after death, they’re reborn in a good place, a heavenly realm.
AN4.85:5.6: That’s how a person is light and bound for light.
AN4.85:5.7: These are the four people found in the world.”
And even if someone is living in poor conditions, and this is due to their past kamma, there is no reason not to help them. This sort of argument has been used so often by the privileged against the underprivileged, and I don’t think that by doing so one is creating particularly good karma for oneself… maybe such people belong to the “light bound for darkness”?
(And as a little personal aside: SuttaCentral Voice is dedicated to the dark bound for light… 
)
Even that monk has come into his bad situation because of his own actions—actions in this very life that ripened as “instant karma”, so to speak: He had never helped the other monks, and now they didn’t look after him in his illness. Which was why the Buddha found him in this desperate condition. And he firmly rebuked the monks for their behavior afterwards! But first he helped the sick monk.
(This story is told in the Vinaya, and I can’t remember the reference right now.)