zuótiān wǎnshang wǒ méi shuìhǎo, suǒyǐ jīntiān yǒudiǎnr tóuténg.

In Mandarin, time words often come before the subject or right after it.

So all of these are natural:

• 昨天晚上我没睡好。
• 我昨天晚上没睡好。

Both mean the same thing. Chinese often likes to set the time frame first, then say who did the action and what happened.

A very common basic pattern is:

Time + Subject + Verb Phrase

So here:

• 昨天晚上 = last night
• 我 = I
• 没睡好 = didn’t sleep well

没 is usually used to negate past or completed actions, while 不 is usually used for habitual actions, general statements, or future intentions.

So:

• 我没睡好 = I didn’t sleep well
• 我不睡好 = not natural for this meaning

In this sentence, the speaker is talking about last night, so it is a past event. That is why 没 is the correct choice.

A useful rule:

• 没 = did not / have not
• 不 = do not / does not / will not / generally not

Here, 好 is not simply the adjective good by itself. It is acting as a result complement after the verb 睡.

So:

• 睡 = to sleep
• 睡好 = to sleep well / to get good sleep / to sleep satisfactorily

Then:

• 没睡好 = didn’t sleep well / didn’t get good sleep

This pattern is very common in Mandarin:

• 吃好 = eat well
• 写好 = write well / finish writing properly
• 做好 = do well / complete properly

So 好 after a verb often suggests that the action was done successfully, properly, or to a satisfactory degree.

Because 没 normally replaces the need for 了 when you are negating a completed action.

Compare:

• 我睡好了。 = I slept well / I’ve gotten good sleep.
• 我没睡好。 = I didn’t sleep well.

In standard Mandarin, you generally do not say 没睡好了 for this meaning.

Also, the time word 昨天晚上 already makes it clear that this happened in the past, so 了 is not necessary.

Yes, 所以 means so or therefore. It introduces the result of what was said before.

Structure:

Cause, 所以 Result

In this sentence:

• 昨天晚上我没睡好 = cause
• 所以今天有点儿头疼 = result

So the logic is:

I didn’t sleep well last night, so I have a bit of a headache today.

In everyday speech, Mandarin speakers sometimes omit 所以 if the relationship is already obvious, but including it makes the connection very clear.

Because in Chinese, the subject is often omitted when it is already obvious.

The full version could be:

• 昨天晚上我没睡好，所以我今天有点儿头疼。

But once 我 has already been established in the first clause, it is very natural to leave it out in the second clause.

This kind of omission is extremely common in Mandarin and sounds very natural.

有点儿 means a little bit, somewhat, or kind of. It often appears before something unpleasant or undesirable.

So:

• 有点儿头疼 = have a bit of a headache / feel somewhat headachey

This sounds more natural and softer than making it sound very severe.

A useful comparison:

• 有点儿累 = a little tired
• 有点儿冷 = a little cold
• 有点儿不舒服 = a little uncomfortable

A common learner point:

• 有点儿 often carries a slight negative feeling
• 一点儿 often means a small amount

So here, 有点儿头疼 is more natural than 一点儿头疼.

Because 头疼 here works as a predicate describing a physical condition, and Chinese does not use 是 the way English uses to be in sentences like I am tired or I am sick.

So Mandarin says:

• 我头疼。 = I have a headache / My head hurts.
• 我今天有点儿头疼。 = I have a bit of a headache today.

But not:

• 我是头疼。 = incorrect for this meaning

This is a very important difference from English. In Mandarin, many words describing states or conditions can directly form the predicate without 是.

It behaves somewhat like a state verb or predicate describing a condition.

Literally:

• 头 = head
• 疼 = ache / hurt

So 头疼 means the head aches or to have a headache.

In English, we often need a separate structure like have a headache, but Chinese can simply say:

• 我头疼。

That is one reason Mandarin can feel very compact compared with English.

You may also see 头痛, which means the same thing. 头疼 is very common in everyday speech.

Yes. That is also natural.

For example:

• 所以今天我有点儿头疼。
• 所以我今天有点儿头疼。
• 今天我有点儿头疼。

These all work. The difference is mostly focus:

• 今天 earlier in the sentence can emphasize today
• 我 earlier can emphasize I

Chinese word order has some flexibility, especially with time words, as long as the sentence remains clear.

Yes, in everyday speech 晚上 is commonly pronounced wǎnshang, with 上 in a neutral tone.

So although you may learn the full tone of 上 in other contexts, in this word it is often light:

• 晚上 → wǎnshang

Also, 有点儿 is often pronounced with erhua:

• yǒudiǎnr

The 儿 is not usually pronounced as a full separate syllable here. It attaches to 点.

So the sentence sounds roughly like:

Zuótiān wǎnshang wǒ méi shuìhǎo, suǒyǐ jīntiān yǒudiǎnr tóuténg.

Yes. You could say:

因为昨天晚上我没睡好，所以今天有点儿头疼。

That means:

Because I didn’t sleep well last night, I have a bit of a headache today.

So:

• 因为 introduces the cause
• 所以 introduces the result

In the original sentence, 因为 is simply omitted because the cause is already obvious from context. That is very common in natural Mandarin.