Custa-me levantar-me cedo ao domingo, porque gosto de dormir mais.

Because custar does not only mean to cost money. It can also mean to be difficult or to require effort.

In this structure:

• Custa-me + infinitive
• literally: It is difficult for me to...

So:

• Custa-me levantar-me cedo = It is hard for me to get up early

The me is an indirect object pronoun meaning to me / for me.

A very literal breakdown would be:

• Custa = is difficult / costs effort
• -me = to me
• levantar-me cedo ao domingo = getting myself up early on Sunday/Sundays

Natural English usually changes the structure to:

• I find it hard to get up early on Sundays.

In European Portuguese, object pronouns are very often placed after the verb in affirmative main clauses. This is called enclisis.

So you get:

• custa-me
• diz-me
• leva-o

And in writing, the pronoun is linked to the verb with a hyphen.

This is very typical of Portugal Portuguese. An English speaker may notice that this often looks different from Brazilian Portuguese, where pronouns are often placed before the verb in everyday usage.

Because the two mes do different jobs.

1) Custa-me

This me means to me / for me. It shows who experiences the difficulty.

2) levantar-me

This me belongs to the verb levantar-se, which means to get up.

So:

• Custa-me = it is hard for me
• levantar-me = to get myself up / to get up

They are not duplicates by mistake. They refer to different grammatical functions.

If you mean get up, normally no. You should keep the reflexive pronoun:

• levantar-me = to get up

Without the reflexive pronoun, levantar usually means to lift, to raise, or to pick up something.

So:

• levantar-me cedo = to get up early
• levantar cedo does not naturally mean the same thing

This is important because many daily-action verbs in Portuguese are reflexive:

• levantar-se = to get up
• deitar-se = to lie down / go to bed
• sentar-se = to sit down

Both orders can exist in Portuguese depending on the grammar around them, but in European Portuguese, after an infinitive, attaching the pronoun to the infinitive is very common and standard:

• levantar-me
• sentar-me
• deitar-me

So Custa-me levantar-me cedo is perfectly normal in European Portuguese.

Here ao domingo expresses a habitual action, so it means:

• on Sundays
• on Sunday in the sense of every Sunday

This is very common in European Portuguese.

So:

• ao domingo = on Sundays / every Sunday

If you want to talk about one specific Sunday, you would normally say:

• no domingo = on Sunday / on the Sunday

For example:

• Ao domingo durmo mais. = On Sundays, I sleep more.
• No domingo tenho um almoço de família. = On Sunday, I have a family lunch.

That is just how Portuguese often expresses repeated time habits.

European Portuguese frequently uses:

• à segunda-feira = on Mondays
• ao sábado = on Saturdays
• ao domingo = on Sundays

So even though English often uses the plural, Portuguese can use the singular with the article and preposition to express a repeated routine.

It is not strange at all; it is the normal idiomatic pattern.

Because the verb gostar normally requires the preposition de.

So you say:

• gosto de café
• gosto de música
• gosto de dormir
• gosto de ler

This is a very important pattern to memorise:

• gostar de + noun
• gostar de + infinitive

So:

• gosto de dormir mais = I like sleeping more / I like to sleep longer

Literally, mais means more. But with dormir, English often translates it more naturally as longer.

So:

• dormir mais = sleep more
• in natural English here: sleep longer

That is why the whole sentence can sound more natural in English as:

• I find it hard to get up early on Sundays because I like to sleep longer.

If you want to be more explicit in Portuguese, you could also say things like:

• dormir mais tempo = sleep for more time
• dormir até mais tarde = sleep until later

Because porque is the normal conjunction meaning because.

So:

• ..., porque gosto de dormir mais. = ..., because I like to sleep longer.

Very simply:

• porque = because
• por que is usually used in questions or other specific structures

For a learner, the main thing to remember is: when you mean because, use porque.

Because cedo modifies the action levantar-me and this position is very natural in Portuguese.

• levantar-me cedo = to get up early

Portuguese adverbs can sometimes move around, but this order is the most straightforward and idiomatic here.

Compare:

• levantar-me cedo = natural
• cedo levantar-me = much less natural in normal speech

So the sentence sounds normal and well-ordered as it is.

Yes. It sounds very natural in Portugal Portuguese.

A few features that feel especially European Portuguese are:

• custa-me with enclisis
• levantar-me
• ao domingo for a habitual Sunday action

A speaker in Portugal would understand this immediately as a normal, idiomatic sentence.