Ako upala ne prođe, doktorica će opet provjeriti je li to infekcija.

This is normal in Croatian.

After ako (if), Croatian usually uses the present tense to talk about a real future condition:

• Ako upala ne prođe... = If the inflammation doesn’t go away...

The main clause then shows the future result:

• doktorica će opet provjeriti... = the doctor will check again...

So the pattern is often:

• Ako + present, future

This is different from English, but actually English does something similar too:

• If it doesn’t improve, the doctor will check again.

Not:

• If it won’t improve...

Prođe comes from the verb proći.

In this sentence, proći means something like:

• to pass
• to go away
• to clear up

So upala ne prođe means the inflammation does not go away / does not clear up.

A useful point: proći is a perfective verb. That means it focuses on a completed result. Here, the idea is not just it is not improving, but it does not fully pass/clear up.

That is why Croatian uses proći very naturally in medical contexts like this.

Upala is in the nominative singular because it is the subject of ne prođe.

• upala = inflammation
• grammatical gender: feminine
• number: singular
• case: nominative

You can see it is the thing doing the “going away”:

• Upala ne prođe. = The inflammation doesn’t go away.

So there is no special case ending here beyond the normal dictionary form.

Doktorica is the feminine form, so it means female doctor.

• doktor = male doctor / doctor in a general sense
• doktorica = female doctor

Since the sentence specifically refers to a woman, Croatian uses doktorica.

You may also see liječnica, which also means female doctor and is often felt to be a bit more formal or more specifically medical. In everyday speech, doktorica is extremely common.

Yes. This is the future tense.

Croatian future 1 is formed with:

• a form of htjeti used as a clitic: ću, ćeš, će, ćemo, ćete, će
• plus the infinitive

Here:

• će = will
• provjeriti = check

So:

• doktorica će provjeriti = the doctor will check

The word će is a clitic, so it normally comes in the second position of the clause. That is why it appears after doktorica:

• Doktorica će opet provjeriti...

If the infinitive came first, you could also get forms like:

• Provjerit će...

But with the subject first, doktorica će... is the normal pattern.

Opet means again.

In this sentence:

• doktorica će opet provjeriti = the doctor will check again

Its position is natural and neutral. Croatian word order is fairly flexible, so you may also hear other placements depending on emphasis, for example:

• Doktorica će opet provjeriti...
• Doktorica će provjeriti opet...
• Opet će doktorica provjeriti...

But they do not all feel equally neutral. In most ordinary situations, će opet provjeriti sounds very natural.

Here je li means whether.

The phrase:

• provjeriti je li to infekcija

means:

• to check whether it is an infection

This is an embedded yes/no question. Compare:

• Direct question: Je li to infekcija? = Is that an infection?
• Embedded question: Provjerit će je li to infekcija. = She will check whether it is an infection.

So je li is not really being translated word-for-word here; functionally, it introduces the idea whether / if.

This is a very common learner question because English uses if both for conditions and for whether-type clauses.

Croatian separates these more clearly:

• ako = if in a condition
  
  • Ako upala ne prođe... = If the inflammation doesn’t go away...
• je li = whether / if in an embedded yes/no question
  
  • provjeriti je li to infekcija = check whether it is an infection

About da li:

• da li is common in speech and widely understood
• but je li is often preferred in more careful standard Croatian

So in this sentence, je li is a very good standard choice.

Because infekcija is not the object of the sentence here. It is a predicate noun after biti (to be).

The structure is:

• to je infekcija = that/it is an infection

Here:

• to = subject-like pronoun (that / it)
• infekcija = noun identifying what to is

So infekcija stays in the nominative.

This is similar to English:

• It is an infection

where an infection is not a direct object, but something that identifies it.

To literally means that, but in sentences like this it often works more like English it.

So:

• je li to infekcija = whether it is an infection

What exactly to refers to depends on context. It could refer to:

• the inflammation
• the symptoms
• the condition/problem being discussed

Croatian often uses to very naturally in this kind of diagnostic statement.

Because the sentence begins with a subordinate clause:

• Ako upala ne prođe, ...

That ako clause is separated from the main clause by a comma.

So the structure is:

• subordinate clause: Ako upala ne prođe
• main clause: doktorica će opet provjeriti je li to infekcija

This comma is standard Croatian punctuation.

Yes. Croatian normally makes verbal negation by putting ne before the finite verb.

So:

• prođe = it goes away / passes
• ne prođe = it does not go away / does not pass

This is very regular in Croatian:

• zna → ne zna
• ima → nema (an irregular contraction)
• dolazi → ne dolazi

Here the negative is straightforward:

• upala ne prođe

Yes. A more literal translation of proći would be to pass.

So word-for-word-ish:

• Ako upala ne prođe = If the inflammation does not pass

But in natural English, especially in a medical context, you would more likely say:

• If the inflammation doesn’t go away
• If the inflammation doesn’t clear up

So pass is closer to the Croatian verb itself, while go away or clear up is usually better English.