uisaga jeungsangi simhaejimyeon geomsareul bada borago haesseo.

Because the sentence contains a main clause and an embedded clause.

• 의사가 ... 했어 = The doctor said ...
• 증상이 심해지면 = if the symptoms get worse

So each clause has its own subject:

• 의사가 = the doctor, subject of 했어
• 증상이 = the symptoms, subject of 심해지면

This is very common in Korean. English also does something similar:

• The doctor said the symptoms would get worse.

There are really two separate actions/events being described, so two subjects are natural.

-면 means if or when.

So:

• 심해지면 = if it gets worse / when it gets worse

In this sentence, it gives a condition:

• 증상이 심해지면 = if the symptoms get worse

A useful thing to remember is that -면 often introduces a condition without strongly forcing a distinction between English if and when. Context tells you which sounds better in translation.

It breaks down like this:

• 심하다 = to be severe
• 심해지다 = to become severe / to worsen
• 심해지면 = if it becomes severe / if it worsens

So -아/어지다 often means to become ...

Examples:

• 좋아지다 = to become good / get better
• 나빠지다 = to become bad / get worse
• 심해지다 = to become severe

So 증상이 심해지면 is very naturally if the symptoms worsen.

In Korean, 검사를 받다 literally means to receive an examination/test, and this is the normal way to say to get examined or to undergo testing.

• 검사 = examination, test
• 받다 = to receive

So:

• 검사를 받다 = to receive an examination
• natural English translation: to get tested, to have an examination, to get checked

By contrast, 검사하다 usually means to inspect/examine something from the examiner’s point of view. For example, a doctor or technician may 검사하다 a patient or sample.

So in this sentence, the patient is the one receiving the test, which is why 검사를 받다 is the natural phrasing.

Here, 보다 is the auxiliary verb that adds the nuance of trying something.

So:

• 검사를 받다 = to get an examination
• 검사를 받아 보다 = to try getting an examination / to go ahead and get examined

In real English, we usually would not translate 보다 literally as try every time. In this sentence, it makes the doctor’s advice sound a bit softer and more like:

• You should try getting tested
• Go get checked out
• Have an examination

So 받아 보라고 했어 has a slightly less blunt tone than just 받으라고 했어.

Also, the standard spacing is often written as 받아 보라고, because 보다 is functioning as an auxiliary after the main verb.

Here, -라고 하다 is being used to report a command, suggestion, or instruction.

So:

• 검사를 받아 보라고 했어 = said to get an examination / told me-you to get checked

This is different from plain statement quoting like -다고 하다.

Compare:

• 온다고 했어 = said that he/she is coming
• 오라고 했어 = said to come / told someone to come

In your sentence, the doctor is not just stating information. The doctor is advising or instructing someone to do something if the symptoms get worse.

Korean often leaves that out when it is clear from context.

So 의사가 ... 검사를 받아 보라고 했어 literally gives:

• The doctor said to get tested if the symptoms get worse

But it does not explicitly say:

• told me
• told you
• told him/her

In real conversation, that person is often understood from context. If you are talking about your own doctor visit, listeners will usually assume the doctor told you.

So Korean is more comfortable than English with omitting understood participants.

이/가 and 은/는 can both appear with subjects, but they give different nuances.

Here, 증상이 심해지면 is a neutral conditional clause:

• if the symptoms get worse

Using -이/가 simply marks 증상 as the subject of 심해지다.

If you said 증상은 심해지면, it would sound more contrastive or topical, something like:

• as for the symptoms, if they get worse...

That is not impossible, but it adds a special emphasis that is not really needed here. So 증상이 is the more natural default choice.

No. 했어 is casual, informal speech.

The base verb is:

• 하다 = to do
• past casual: 했어 = did / said

So the sentence ends in a casual style that you would use with:

• close friends
• younger people
• someone you speak casually with
• diary-style narration

Polite versions would be:

• 의사가 증상이 심해지면 검사를 받아 보라고 했어요.
• more formal: 의사가 증상이 심해지면 검사를 받아 보라고 했습니다.

The grammar stays the same; only the speech level changes.

Yes, -면 can sometimes be interpreted as when depending on context.

In this sentence, both are possible in principle:

• if the symptoms get worse
• when the symptoms get worse

But in a doctor’s instruction, English usually prefers if, because it sounds like a condition that may or may not happen.

So the most natural translation is usually:

• The doctor said to get tested if the symptoms get worse.

를 marks the direct object.

• 검사 = examination / test
• 검사를 = the examination/test as the object

It is the object of 받다:

• 검사를 받다 = to receive an examination

So even though English says get examined or get tested, Korean structures it as receive + examination, which is why 검사 takes the object marker 를.

Both can mean that the doctor told someone to get an examination, but the nuance is a little different.

• 검사를 받으라고 했어 = told me-you to get an examination
• 검사를 받아 보라고 했어 = told me-you to try getting an examination

Adding 보다 often softens the wording and can make it sound more like advice or a recommendation rather than a direct command.

So in many contexts:

• 받으라고 했어 sounds more direct
• 받아 보라고 했어 sounds slightly gentler, like you should try getting checked

Using 의사가 simply identifies the doctor as the subject of said.

• 의사가 했어 = the doctor said it

If you used 의사는, it would usually add topic or contrast, such as:

• As for the doctor, he said...
• The doctor, at least, said...

That is possible in the right context, but with no special contrast intended, 의사가 is the neutral and natural choice.

Yes. Even though -라고 하다 can report commands, in context it often covers a range from:

• command
• instruction
• recommendation
• advice

Because this is a doctor speaking, English often translates it more naturally as advice:

• The doctor said to get tested if the symptoms get worse.
• The doctor told me to get checked out if the symptoms get worse.
• The doctor said I should get an examination if the symptoms get worse.

So the Korean does not have to sound harsh. The exact force depends on context and tone.