yīshēng shuō wǒ chī le yào yǐhòu yào duō xiūxi.

Chinese often puts the topic or setting first, then the main action.

So this sentence is structured like:

• 医生说 = the doctor said
• 我吃了药以后 = after I take/took the medicine
• 要多休息 = need to rest more

A natural way to think of it is:

• The doctor said [that] after I take the medicine, I need to rest more.

Chinese does not need a word like that here. The clause after 说 simply gives the content of what was said.

In this sentence, 说 most literally means said, but in natural English the whole sentence may be translated as The doctor told me... depending on context.

Chinese 说 by itself does not explicitly include an object like me. It just introduces speech.

So:

• 医生说... = The doctor said...
• 医生跟我说... / 医生对我说... = The doctor said to me... / told me...

In your sentence, 我 belongs to the content of what was said, not to 说.

The 了 after 吃 marks the action as completed.

• 吃药 = take medicine / eat medicine
• 吃了药 = took the medicine / have taken the medicine

So:

• 吃了药以后 = after taking the medicine / after I have taken the medicine

This 了 is attached to the verb phrase and shows completion of that action. It is not the sentence-final 了 that changes the overall situation or mood.

以后 means after or afterward.

In this sentence:

• 吃了药以后 = after taking the medicine

A common pattern is:

• Verb phrase + 以后 = after doing something

Examples:

• 吃饭以后 = after eating
• 下课以后 = after class ends
• 回家以后 = after going home

So 我吃了药以后 literally means after I have taken the medicine.

Because 以后 attaches to the event that happens first.

So Chinese builds it like this:

• 吃了药 = take the medicine
• 吃了药以后 = after taking the medicine

You cannot place 以后 before 吃了药 in the same way if you want this meaning. It comes after the action phrase it refers to.

Here 要 means need to / should rather than want to.

So:

• 要多休息 = need to rest more / should get more rest

The exact English wording depends on context, but in a doctor’s advice, 要 usually sounds like need to or should, not want to.

Compare:

• 我要喝水。 = I want to drink water. / I’m going to drink water.
• 你感冒了，要多休息。 = You have a cold; you should rest more.

Yes, that is completely normal in Chinese. Many characters share the same pronunciation.

Here:

• 药 = medicine
• 要 = to want / to need / to be going to

They are both pronounced yào in Mandarin, but the meaning is clear from context.

In this sentence:

• 吃了药 = took medicine
• 要多休息 = need to rest more

This kind of homophone is very common in Chinese.

多 here means more, and it modifies the verb 休息.

So:

• 休息 = rest
• 多休息 = rest more / get more rest

In Chinese, adverbs usually come before the verb, so 多 appears before 休息.

Compare:

• 多吃一点 = eat a bit more
• 多喝水 = drink more water
• 多练习 = practice more

Yes. In this sentence, 休息 is a verb meaning to rest.

• 要多休息 = need to rest more

But in English, this is often translated with the noun rest:

• You need more rest.

That is just a difference in how English and Chinese naturally express the idea.

Grammatically in Chinese, 我 does not change form the way English pronouns do.

So 我 can correspond to:

• I
• me

depending on the sentence.

Here, 我 is the subject of the clause:

• 我吃了药以后 = after I take the medicine

If the doctor were explicitly speaking to me, Chinese would more likely say something like:

• 医生跟我说... = The doctor said to me...

It contains both a completed action and advice about what should happen next.

• 吃了药 = taking the medicine is viewed as completed
• 以后 = after that
• 要多休息 = then one should rest more

So the meaning is roughly:

• After taking the medicine, I need to rest more.

Depending on context, English may say:

• After I take the medicine, I should rest more.
• After I took the medicine, the doctor said I should rest more.

Chinese often leaves some tense details to context rather than marking them as strictly as English does.

Yes, but the meaning would shift slightly.

• 吃了药以后 = after taking the medicine / after having taken the medicine
• 吃药以后 = after taking medicine / after taking the medicine

Without 了, the action is less explicitly marked as completed. In many contexts both are possible, but 吃了药以后 makes the sequence a bit clearer: first take the medicine, then rest more.

No. Another common word is 之后.

For example:

• 吃了药以后要多休息。
• 吃了药之后要多休息。

Both mean roughly After taking the medicine, you should rest more.

In everyday speech, 以后 is very common and natural. The difference between 以后 and 之后 is often small in sentences like this.