Miệng tôi đau.

In Vietnamese, possession usually works as:

noun + possessor

So:

• miệng tôi = my mouth
• nhà tôi = my house
• bạn tôi = my friend

That is why Miệng tôi đau literally looks like mouth my hurts.

Vietnamese often does not use a word like English is in this kind of sentence.

Here, đau means hurt / painful / sore, and it can directly describe the subject:

• Miệng tôi đau. = My mouth hurts.

So this is normal Vietnamese structure. You do not need là here.
In fact, Miệng tôi là đau would be wrong.

It behaves like a stative verb or predicate adjective, depending on how you like to think about Vietnamese grammar.

In practical terms, the important point is:

• đau can be the main predicate by itself
• it means something like to hurt / to be painful / sore

So:

• Tôi đau đầu. = I have a headache / My head hurts
• Miệng tôi đau. = My mouth hurts

You do not need another verb.

Yes, Tôi đau miệng is also possible and very common.

There is a small difference in focus:

• Miệng tôi đau. = emphasizes my mouth
• Tôi đau miệng. = emphasizes I and says that the pain is in the mouth

Both can mean My mouth hurts.

In everyday speech, learners will often hear symptom patterns like:

• Tôi đau đầu. = I have a headache.
• Tôi đau bụng. = My stomach hurts.
• Tôi đau miệng. = My mouth hurts.

So Tôi đau miệng may feel especially natural in many situations.

Because classifiers are not always required.

For body parts, especially in simple statements like this, Vietnamese often just uses the noun directly:

• miệng tôi đau
• tay tôi đau
• mắt tôi đau

You can sometimes hear cái miệng, but that usually sounds more specific, contrastive, or expressive, not neutral.

So for a simple statement like My mouth hurts, Miệng tôi đau is perfectly normal.

Yes, miệng is a tricky word for English speakers.

A rough guide:

• miệng sounds somewhat like mee-uhng in the North, but that is only approximate
• it has the nặng tone, which is a low, short, heavy tone

A few pronunciation notes:

• iê is a vowel combination
• ng is the final sound like in English sing
• the tone on ệ makes the syllable short and heavy

The whole sentence has these tones:

• Miệng — nặng tone
• tôi — ngang tone
• đau — ngang tone

If you want a simple learner-friendly approximation:

• Miệng tôi đau ≈ mee-ung toy dow

But that is only a rough pronunciation aid, not an exact pronunciation.

Not always. Tôi is a common, neutral word for I / me, and after a noun it can mean my.

But Vietnamese pronouns depend a lot on relationship, age, and politeness. So other words can replace tôi:

• miệng em đau = my mouth hurts (said by someone using em)
• miệng anh đau = my mouth hurts (said by a man using anh)
• miệng con đau = my mouth hurts (said by a child using con)

So tôi is safe and useful, but not the only option.

Miệng means mouth. It does not specifically mean lips.

If you want to say lips, the word is:

• môi = lips

So:

• Miệng tôi đau. = My mouth hurts.
• Môi tôi đau. = My lips hurt.

This distinction matters, especially when describing pain or medical symptoms.

Yes, a Vietnamese speaker can absolutely say Miệng tôi đau.

But depending on context, other natural versions include:

• Tôi đau miệng.
• Miệng tôi bị đau.
• Tôi bị đau miệng.
• Miệng tôi đau quá. = My mouth hurts a lot.

A quick nuance guide:

• Miệng tôi đau: simple statement
• Tôi đau miệng: very common symptom pattern
• bị đau: can sound a bit more explicitly like to be suffering from pain
• quá: adds emphasis, like really or so much

Yes. To say My mouth doesn’t hurt, you can say:

• Miệng tôi không đau.

Here, không goes before đau.

So:

• Miệng tôi đau. = My mouth hurts.
• Miệng tôi không đau. = My mouth doesn’t hurt.

That same pattern works with many descriptive words in Vietnamese.

Yes, very easily.

Examples:

• Miệng tôi đau lắm. = My mouth hurts a lot.
• Miệng tôi đau quá. = My mouth hurts so much.
• Miệng tôi đang đau. = My mouth is hurting right now.
• Miệng tôi đau từ sáng. = My mouth has hurt since morning.

Vietnamese often builds on a short base sentence like Miệng tôi đau by adding small words after or before the predicate.