Hôm nay tôi đau đầu nên muốn đến hiệu thuốc sau giờ làm.

In Vietnamese, time expressions very often go at the beginning of the sentence to set the time frame for everything that follows.

So Hôm nay tôi đau đầu... feels very natural: it means something like As for today / Today, I have a headache...

You could sometimes place hôm nay elsewhere, but sentence-initial position is the most common and natural here.

Yes, literally it is built from:

• đau = hurt, painful, ache
• đầu = head

Together, đau đầu means to have a headache or headache depending on context.

Vietnamese often expresses body problems this way:

• đau đầu = have a headache
• đau bụng = have a stomachache
• đau lưng = have back pain

So instead of using a structure like I have a headache, Vietnamese often just says I head-hurt.

Because the subject is already clear.

In Hôm nay tôi đau đầu nên muốn đến hiệu thuốc..., the understood subject of muốn is still tôi. Vietnamese often omits repeated subjects when there is no confusion.

So this is understood as:

• Hôm nay tôi đau đầu nên (tôi) muốn đến hiệu thuốc sau giờ làm.

Repeating tôi is possible, but omitting it sounds smoother and more natural here.

Nên means so, therefore, or that’s why.

It links the cause and the result:

• đau đầu = having a headache
• nên muốn đến hiệu thuốc = so want to go to the pharmacy

A useful pattern is:

• vì..., nên... = because..., so...

But in natural speech, Vietnamese often drops vì if the cause is already obvious. That is what happens here.

So:

• Tôi đau đầu nên muốn đến hiệu thuốc.

  is a natural way to say:

• I have a headache, so I want to go to the pharmacy.

Yes. Muốn means want, want to, or sometimes would like to, depending on context.

In this sentence, muốn đến hiệu thuốc means want to go to the pharmacy.

A few notes:

• muốn is neutral and very common
• it can express a real desire, intention, or plan
• it is not overly strong here

So this sentence sounds natural, not dramatic.

Đến means to come/go to, to reach, or to arrive at a place. It focuses on the destination.

So:

• đến hiệu thuốc = go to the pharmacy / come to the pharmacy

Vietnamese does not always need a separate word like đi before đến. Using just đến is enough.

Compare:

• đi = go
• đến = go/come to, arrive at

In this sentence, đến hiệu thuốc is perfectly natural because the destination is what matters.

Hiệu thuốc means pharmacy or drugstore.

However, Vietnamese also commonly uses:

• nhà thuốc
• sometimes tiệm thuốc in some contexts or regions

All of these can refer to a place where you buy medicine, though usage can vary by region and style.

For a learner, the important point is:

• hiệu thuốc is correct and understandable
• nhà thuốc is also very common in modern Vietnamese

Literally, it means:

• sau = after
• giờ = hour/time
• làm = work

So sau giờ làm means after work or after working hours.

It is a compact Vietnamese expression. English often needs extra words, but Vietnamese can leave them implied.

A fuller version would be:

• sau giờ làm việc

That is a bit more explicit, but sau giờ làm is very natural in everyday speech.

Vietnamese does not use articles the way English does, so words like a and the are usually not translated directly.

Also, possession is often left implicit when it is obvious.

For example:

• đau đầu already clearly means my head hurts / I have a headache
• đến hiệu thuốc does not need a word for the pharmacy unless you want to specify a particular one

So Vietnamese relies more on context than English does.

Yes, it is natural and easy to understand.

It sounds like a neutral, everyday sentence. A native speaker might also say slightly different versions, such as:

• Hôm nay tôi bị đau đầu nên muốn đến hiệu thuốc sau giờ làm.
• Hôm nay tôi đau đầu nên muốn ghé hiệu thuốc sau giờ làm.

Nuance:

• bị đau đầu sounds a little more explicit: am suffering from a headache
• ghé hiệu thuốc suggests stop by the pharmacy

But your original sentence is already good natural Vietnamese.

Yes. Tôi is a neutral, standard word for I. It is a safe choice in many situations, especially for textbook sentences.

But Vietnamese pronouns change depending on relationship, age, and social context. In real life, a speaker might say:

• em if speaking to someone older
• mình in some casual contexts
• anh or chị depending on who is speaking

So tôi is grammatically correct and neutral, but it is not the only possible first-person pronoun.