uisaga jusareul majeulji mureossjiman naneun yakman meokgessdago haesseo.

-가 marks 의사 as the grammatical subject of 물었지만.

So 의사가 물었지만 means the doctor asked, but...

If you said 의사는, it would sound more like as for the doctor, ... and would shift the topic slightly. Both can be possible in real conversation, but 의사가 is a very natural choice here because it simply introduces who did the asking.

주사를 맞다 is the standard Korean expression for to get an injection / receive a shot.

Even though 맞다 often means to be hit, it can also mean to receive something physically administered, such as:

• 주사를 맞다 = get a shot
• 예방접종을 맞다 = get vaccinated

So you should learn 주사를 맞다 as a set phrase rather than translating 맞다 literally.

맞을지 is 맞다 + -(으)ㄹ지, which means whether or whether to in an indirect-question sense.

So 주사를 맞을지 물었다 means:

• asked whether I would get a shot
• asked if I wanted to get a shot

It does not mean the doctor literally asked a yes/no question using the exact English structure Will you get a shot? It is a reported, indirect question.

This is about nuance.

• 맞는지 asks whether something is true or happening
• 맞을지 asks about a future possibility, intention, or choice

Here, the doctor is asking about a decision that has not happened yet: whether the speaker will get an injection. That is why 맞을지 fits better.

So:

• 주사를 맞는지 물었다 = asked whether I am getting / do get a shot
• 주사를 맞을지 물었다 = asked whether I would get a shot

The hidden subject is I / me, understood from context.

Korean often leaves out subjects when they are obvious. In this sentence, the doctor is asking the speaker whether the speaker will get an injection, so there is no need to repeat 내가.

A more explicit version could be:

• 의사가 내가 주사를 맞을지 물었지만...

But that sounds unnecessarily heavy in normal conversation. Omitting it is much more natural.

물었지만 is:

• 묻다 = to ask
• 물었- = past tense
• -지만 = but / although

So 물었지만 means asked, but...

It connects the first clause and the second clause:

• 의사가 주사를 맞을지 물었지만
• 나는 약만 먹겠다고 했어

Together: The doctor asked whether I’d get a shot, but I said I’d only take medicine.

만 means only / just.

So:

• 약 = medicine
• 약만 = only medicine / just medicine

This shows contrast with the injection:

• not a shot
• only medicine

It gives the sentence the nuance of I said I would only take medicine instead.

먹겠다고 했어 is reported speech built from:

• 먹겠다 = I will eat / I’ll take / I intend to take
• -고 하다 = to say that...

So 먹겠다고 했어 means I said that I would take it or I said I’d take it.

Here -겠- expresses the speaker’s will or intention. It sounds like a decision:

• 나는 약만 먹겠다고 했어 = I said I would only take medicine

This is very natural when reporting your own decision or refusal.

Yes, 먹다 literally means to eat, but in Korean it is also used for taking medicine by mouth.

So:

• 약을 먹다 = take medicine
• 밥을 먹다 = eat a meal

This is completely normal Korean usage. English separates eat and take here, but Korean uses 먹다 for both food and oral medicine.

Yes, but the nuance changes a little.

• 먹겠다고 했어 emphasizes intention or determination
• 먹을 거라고 했어 sounds more like a neutral future statement

So:

• 약만 먹겠다고 했어 = I said I’d only take medicine
• 약만 먹을 거라고 했어 = I said I was going to take only medicine

Both are possible, but 먹겠다고 했어 works very well when the speaker is making a choice in response to the doctor.

나는 marks I as the topic of the second clause.

This creates a nice contrast:

• 의사가... 물었지만 = the doctor asked...
• 나는... 했어 = as for me, I said...

So the sentence sets up two sides:

1. what the doctor did
2. what I said in response

Using 나는 makes that contrast clear and natural.

Yes. 했어 is casual, informal speech.

The dictionary form is 하다, and the polite form would be 했어요.

So you could say:

• casual: 의사가 주사를 맞을지 물었지만 나는 약만 먹겠다고 했어.
• polite: 의사가 주사를 맞을지 물었지만 저는 약만 먹겠다고 했어요.

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

Yes, it is natural.

The basic structure is:

• 의사가 = subject
• 주사를 맞을지 = whether to get a shot
• 물었지만 = asked, but
• 나는 = as for me
• 약만 = only medicine
• 먹겠다고 했어 = said I would take

Korean word order is somewhat flexible, but this order is very natural and easy to understand. You could move some topic elements around in conversation, but this version sounds standard and clear.