Minha cabeça dói quando eu durmo pouco.

Because cabeça is a feminine singular noun in Portuguese.

So the possessive has to match the noun being possessed, not the gender of the speaker:

• minha cabeça = my head
• meu braço = my arm

Even if the speaker is male, he would still say minha cabeça, because cabeça is feminine.

Dói is the third-person singular form of the verb doer.

The subject of the sentence is minha cabeça, so the verb agrees with cabeça:

• Minha cabeça dói. = My head hurts.
• Meus olhos doem. = My eyes hurt.

This is different from English, where we often say I have a headache. In Portuguese, it is very normal to make the body part the subject of the verb.

Yes, it is correct and understandable.

That said, many Brazilians would also say things like:

• Fico com dor de cabeça quando durmo pouco.
• Tenho dor de cabeça quando durmo pouco.

These can sound a bit more everyday and idiomatic in some contexts. But Minha cabeça dói quando eu durmo pouco is still perfectly valid.

Because the sentence describes a habitual or general situation.

It means something like:

• whenever I sleep too little, my head hurts

In both English and Portuguese, the present tense is often used for repeated facts or patterns:

• Quando eu durmo pouco, minha cabeça dói.
• When I sleep too little, my head hurts.

It is not only about what is happening right now.

No. You can also say:

• Minha cabeça dói quando durmo pouco.

Portuguese often drops subject pronouns because the verb ending already shows who the subject is:

• durmo already means I sleep

However, eu is often included for:

• emphasis
• clarity
• natural rhythm in speech

So both versions are correct.

Here, pouco means little or not much.

So durmo pouco means:

• I sleep little
• I don’t sleep much
• I sleep too little

In natural English, we often translate it as I don’t get enough sleep.

If you want to make the idea stronger in Portuguese, you could say:

• durmo muito pouco = I sleep very little

Yes, a minha cabeça is also possible.

In Brazilian Portuguese, possessives are often used with an article:

• a minha cabeça
• o meu braço

But the article can also be omitted, especially in shorter, direct sentences. So both are possible:

• Minha cabeça dói.
• A minha cabeça dói.

The version without the article sounds very natural here.

Sometimes, but the meaning changes slightly.

• quando = when / whenever
• se = if

In this sentence, quando suggests a repeated pattern:

• Quando eu durmo pouco, minha cabeça dói. = Whenever I sleep too little, my head hurts.

Using se would make it sound more conditional:

• Se eu durmo pouco, minha cabeça dói.

That is understandable, but quando is more natural here because the speaker is talking about something that regularly happens.

You could, but it sounds less natural for a general habit.

• dói works better for a repeated fact
• está doendo usually focuses on something happening right now or over a current period

So:

• Minha cabeça dói quando eu durmo pouco. = general pattern
• Minha cabeça está doendo. = my head is hurting right now

For the original meaning, dói is the better choice.

Durmo pouco is the normal, neutral word order.

In Portuguese, adverbs like pouco often come after the verb:

• durmo pouco
• como muito
• trabalho bastante

Pouco durmo is possible, but it sounds more emphatic, marked, or literary, as if you are stressing the small amount of sleep.

So for everyday speech, durmo pouco is the natural choice.

A simple approximation is:

• minha ≈ MEEN-ya
• dói ≈ doy

A few details:

• nh in minha is like the ny sound in canyon
• dói is one strong syllable with a diphthong
• the stress is on dói, durmo, and the middle part of cabeça

A rough full pronunciation guide would be:

• Minha cabeça dói quando eu durmo pouco
• MEEN-ya ka-BEH-sa doy KWAN-do ew DOOR-mo POH-ko

Not perfect, but close enough to help you get started.