Kiedy boli mnie nos, piję gorącą herbatę, a moje usta są suche.

In Polish, the verb boleć often works a bit differently from English to hurt.

• Boli mnie nos literally works like My nose hurts me.
• mnie is the person who feels the pain.
• nos is the body part that hurts.

This pattern is very common in Polish:

• Boli mnie głowa = I have a headache / My head hurts.
• Bolą mnie oczy = My eyes hurt.

You can say mój nos boli, but it sounds less natural in everyday speech for physical pain. Boli mnie nos is the normal way.

mnie is in the accusative case here.

With boleć, the person affected by the pain is usually expressed in the accusative:

• boli mnie
• boli cię
• boli go
• boli nas

So in boli mnie nos, mnie means me as the experiencer of the pain.

Because the subject is nos, and nos is singular.

In Polish, the verb agrees with the thing that hurts:

• Boli mnie nos = My nose hurts.
• Boli mnie głowa = My head hurts.
• Bolą mnie oczy = My eyes hurt.
• Bolą mnie uszy = My ears hurt.

So:

• singular body part → boli
• plural body parts → bolą

Because pić takes a direct object, and the direct object usually goes in the accusative case.

The noun herbata is feminine, and in the accusative singular it becomes:

• herbata → herbatę

The adjective must match the noun in gender, number, and case:

• gorąca herbata → nominative
• gorącą herbatę → accusative

So piję gorącą herbatę means I drink hot tea.

piję is the 1st person singular form of pić = to drink.

So:

• piję = I drink
• pijesz = you drink
• pije = he/she/it drinks
• pijemy = we drink

The ending -ę is a very common ending for I in Polish present tense verbs.

Here kiedy means when, but in context it can also feel like whenever.

So the sentence can be understood as:

• When my nose hurts, I drink hot tea, and my lips are dry.
• Depending on context, it may also suggest: Whenever my nose hurts...

In everyday Polish, kiedy is very common for time clauses like this.

Yes, gdy would also work:

• Gdy boli mnie nos, piję gorącą herbatę...

Both mean when. The difference is mostly stylistic:

• kiedy = very common, neutral
• gdy = also common, sometimes a little more formal or literary

For a learner, kiedy is a very safe everyday choice.

Because usta is a plural noun.

In Polish, usta means mouth or lips, but grammatically it is usually treated as plural-only in this meaning.

So the possessive adjective must also be plural:

• moje usta = my lips / my mouth

That is why you get:

• moje, not moja or mój

Because usta is grammatically plural, so the verb must also be plural:

• usta są = the lips are
• not usta jest

And the adjective must match too:

• suche = plural form

So everything agrees:

• moje = plural
• usta = plural
• są = plural
• suche = plural

It can suggest either, depending on context, but in this sentence my lips are dry is the most natural interpretation.

Why?

Because dry lips is a very common idea, while dry mouth would more often be expressed differently, for example:

• Mam sucho w ustach = My mouth is dry / I have a dry mouth

So moje usta są suche will usually be understood as my lips are dry.

The first comma separates the time clause from the main clause:

• Kiedy boli mnie nos, ...
• When my nose hurts, ...

The second comma appears before a, which often connects two clauses and commonly takes a comma in Polish:

• ..., piję gorącą herbatę, a moje usta są suche.

In Polish, commas are often used more regularly before conjunctions introducing another clause than in English.

Usually, yes, a is often translated as and, but it is not exactly the same as i.

Very roughly:

• i = and, simple addition
• a = and/but/while, often with a mild contrast or shift

In this sentence, a links another related statement:

• I drink hot tea, and my lips are dry.

It feels natural because the second part adds another condition or symptom rather than simply listing equal items.

Polish word order is fairly flexible, but some versions sound more natural than others.

The given sentence is perfectly natural:

• Kiedy boli mnie nos, piję gorącą herbatę, a moje usta są suche.

You might also hear:

• Kiedy nos mnie boli, piję gorącą herbatę...

But boli mnie nos is especially common with pain expressions.

In general, Polish changes word order for emphasis, rhythm, or style, but beginners should usually stick to the most common pattern they see.

Most naturally, it sounds habitual or general:

• When my nose hurts, I drink hot tea...

That is because Polish present tense can describe:

• something happening now
• something habitual
• a general truth or repeated situation

So here it sounds like a usual reaction or typical situation, not necessarily just one specific moment.

Yes, and mam suche usta is often more natural in everyday speech.

Compare:

• moje usta są suche = my lips are dry
• mam suche usta = I have dry lips

Both are correct, but mam suche usta is often the more idiomatic everyday way to describe a condition.

Similarly:

• Mam zatkany nos = I have a blocked nose
• Mam spierzchnięte usta = I have chapped lips

So the sentence you were given is correct, but there are other natural ways to say similar things.