Pinggang saya sakit kerana saya tersalah angkat kotak berat semalam.

Pinggang usually means the waist or the lower back/hip area. In this sentence, it refers to the part of the body that hurts after lifting something badly, so English often renders it as lower back or back.

So Pinggang saya sakit is naturally understood as My lower back hurts or My waist/back area hurts.

In Malay, possessive words like saya usually come after the noun.

So:

• pinggang saya = my waist / my lower back
• kotak saya = my box
• rumah saya = my house

This is different from English, where possession usually comes first.

Malay often does not use a verb like is/am/are when describing a state.

So:

• Pinggang saya sakit literally looks like my back painful
• Natural English: My back hurts / My back is sore

This is normal Malay structure. The adjective or state word can function as the predicate without needing is.

Sakit can mean painful, sore, hurt, or ill/sick, depending on context.

In this sentence, it means hurts / is painful:

• Pinggang saya sakit = My lower back hurts

In other contexts:

• Saya sakit = I am sick / ill
• Kaki saya sakit = My leg hurts

So sakit is a very common word used both for illness and pain.

Yes. Saya sakit pinggang is also natural and common.

There is a slight difference in focus:

• Pinggang saya sakit = focuses on the lower back
• Saya sakit pinggang = focuses on me having back pain

Both are correct in everyday Malay.

Kerana means because.

So:

• ... kerana saya tersalah angkat kotak berat semalam = ... because I lifted a heavy box the wrong way yesterday

Yes, in everyday speech, many speakers would also use sebab:

• Pinggang saya sakit sebab saya tersalah angkat kotak berat semalam.

Both are correct.
A rough difference:

• kerana = a bit more formal or written
• sebab = very common in casual speech

Tersalah angkat means something like:

• accidentally lifted it the wrong way
• made a mistake while lifting
• lifted it incorrectly

The important idea is that the action was mistaken, not deliberate.

Here, tersalah adds the sense of doing something wrongly/by mistake, and angkat is lift.

So the sentence suggests the speaker hurt their back because they lifted the heavy box incorrectly.

Malay often allows a structure where tersalah comes before a base verb:

• tersalah cakap = spoke by mistake
• tersalah tekan = pressed by mistake
• tersalah angkat = lifted wrongly / by mistake

So tersalah angkat is a very natural pattern.

You may sometimes also see fuller verbal forms in other contexts, but in everyday Malay, tersalah + base verb is very common and idiomatic.

In Malay, adjectives usually come after the noun.

So:

• kotak berat = heavy box
• rumah besar = big house
• kereta merah = red car

That is why kotak berat is the normal order.

Also, Malay does not require a/the, so kotak berat can mean:

• a heavy box
• the heavy box

Context tells you which is meant.

Yes, kotak yang berat is possible.

Compare:

• kotak berat = heavy box
• kotak yang berat = the box that is heavy / the heavy box

The version without yang is simpler and very common in ordinary noun phrases.
The version with yang can sound a bit more explicit or descriptive.

In this sentence, kotak berat is perfectly natural.

Here, semalam most naturally modifies the lifting event:

• saya tersalah angkat kotak berat semalam = I lifted a heavy box the wrong way yesterday

So the idea is:

• my lower back hurts now
• because yesterday I lifted a heavy box incorrectly

Malay often places time words like semalam near the end of the clause.

Malay does not mark tense the same way English does.

The verb itself does not change like lift / lifted / will lift. Instead, time is usually shown by context or time words such as:

• semalam = yesterday
• hari ini = today
• esok = tomorrow
• sudah = already
• akan = will

In this sentence:

• semalam tells you the lifting happened yesterday
• sakit is understood from context as a present state: the back hurts

So Malay relies heavily on time expressions and context rather than verb endings.

A useful breakdown is:

• Pinggang saya = my lower back / waist
• sakit = hurts / is painful
• kerana = because
• saya = I
• tersalah angkat = accidentally lifted wrongly / lifted the wrong way
• kotak berat = a heavy box
• semalam = yesterday

So the full structure is:

Pinggang saya sakit kerana saya tersalah angkat kotak berat semalam.
= My lower back hurts because I lifted a heavy box the wrong way yesterday.