Min søster siger, at jeg overdriver, når jeg klager over vejret, men jeg er egentlig bare træt.

Because Danish normally does not use the definite ending when a noun already has a possessive word like min, din, hans, vores, and so on.

• min søster = my sister
• not min søsteren

So the possessive already makes the noun specific, and the extra definite ending would usually be wrong here.

Here at means that and introduces a subordinate clause:

• Min søster siger, at jeg overdriver
  = My sister says that I exaggerate

In everyday English, that is often omitted, but in Danish at is very common in this kind of sentence.

Because Danish subordinate clauses do not use normal main-clause inversion. After a conjunction like at, the subject usually comes before the verb:

• at jeg overdriver
• at hun kommer
• at vi er trætte

A useful thing to remember is:

• main clauses often follow verb-second order
• subordinate clauses usually do not

So at jeg overdriver is the expected structure.

For the same reason: når introduces a subordinate clause, and subordinate clauses normally keep the order subject + verb.

• når jeg klager over vejret = when I complain about the weather

If the clause were a main clause, you could get inversion in some contexts, but not here.

Når usually means when in the sense of something that happens repeatedly, generally, or whenever.

Here the idea is:

• when(ever) I complain about the weather

So når fits well because this sounds like a repeated situation.

Compare:

• når = when / whenever, often repeated or general
• da = when, but usually about a specific event in the past
• hvis = if

So in this sentence, når is the natural choice.

The verb is at klage over, which means to complain about. The preposition over is part of the expression.

• klage over noget = complain about something

So:

• jeg klager over vejret = I complain about the weather

This over is not being used literally in a spatial sense. It is just the preposition that goes with klage in this meaning.

Because vejret means the weather, while vejr means weather in a more general sense.

• vejr = weather
• vejret = the weather

Danish usually adds the definite article as an ending:

• et vejr = a weather-type form grammatically, though not very common in everyday use
• vejret = the weather

In this sentence, you are talking about the specific thing people normally complain about, so vejret is the natural form.

Egentlig can mean actually, really, in fact, or sometimes basically, depending on context.

In this sentence, it softens and clarifies the speaker’s point:

• men jeg er egentlig bare træt = but actually I’m just tired = but really I’m just tired

It suggests that the real issue is not dramatic exaggeration; the speaker is simply tired.

Bare often means just or simply.

So:

• jeg er bare træt = I’m just tired

It makes the explanation sound more modest or down-to-earth. Combined with egentlig, it gives a nuance like:

• I’m actually just tired
• I’m really just tired

In a main clause, Danish usually places the finite verb early, and short adverbs like egentlig typically come after that verb.

So:

• jeg er egentlig bare træt

breaks down as:

• jeg = subject
• er = finite verb
• egentlig bare = adverbial words
• træt = adjective

This is very normal Danish word order for a main clause.

Yes. The finite verbs are:

• siger = says / is saying
• overdriver = exaggerate / am exaggerating
• klager = complain / am complaining
• er = am

Danish present tense often covers both simple present and present progressive meanings in English. So:

• jeg klager can mean I complain or I’m complaining, depending on context.

That is why Danish does not need a special -ing form here.

A very common present-tense pattern in Danish is to use -r:

• at klage → klager
• at overdrive → overdriver

So if you know the infinitive, the present tense is often easy to recognize.

Sige is a little less transparent to beginners:

• at sige = to say
• siger = says

But it still has the same present-tense -r ending.

Because the sentence contains several clauses, and Danish writing often marks clause boundaries clearly with commas.

The clauses are:

• Min søster siger
• at jeg overdriver
• når jeg klager over vejret
• men jeg er egentlig bare træt

The når-clause is inserted in the middle, so it is set off with commas. The comma before at is also very common in Danish. Comma practice can vary a little depending on the system used, but this punctuation is perfectly standard and natural for learners to copy.

Yes, træt is an adjective meaning tired.

Here it is used after er, so it is a predicative adjective:

• jeg er træt = I am tired

In this sentence, it stays in the singular form because it refers to one person: jeg. You would see other forms in some other contexts, for example:

• et træt barn = a tired child
• vi er trætte = we are tired

So træt is the correct form here.