Se eu tiver febre de novo, vou ligar para a médica.

Because after se (if) when you’re talking about a possible future situation, Portuguese typically uses the future subjunctive.

• Se eu tiver febre de novo = If I (happen to) have a fever again (in the future)
  The verb ter (to have) in the future subjunctive is: eu tiver, você/ele tiver, nós tivermos, vocês/eles tiverem.

Vou ligar is the near future / “going to” future: ir (present) + infinitive.

• vou ligar = I’m going to call / I will call
  It’s extremely common in Brazilian Portuguese and often preferred over the simple future ligarei (which sounds more formal).

In Brazilian Portuguese, the most common pattern for “to call (someone)” is ligar para + person:

• ligar para a médica = to call the doctor
  You may also see ligar pra (spoken contraction). In some contexts ligar a can appear, but ligar para is the safer, more natural choice in Brazil.

Meaning-wise, they’re the same.

• para a médica = standard / more careful
• pra médica = very common spoken contraction of para a
  In writing (especially formal writing), para a is preferred.

Portuguese often uses a definite article before professions when referring to a specific person.

• a médica = the (female) doctor (a particular doctor)
  You can drop the article in some situations (especially after certain verbs or in more generic statements), but here para a médica sounds natural because it implies a specific doctor you’ll call.

Yes. médica is feminine. If the doctor is male, you’d say:

• o médico
  If you don’t know the doctor’s gender, people often default to o médico (traditional generic) or rephrase (e.g., a pessoa médica is uncommon; more natural would be something like vou ligar para o consultório / para a clínica depending on context).

Approximate pronunciations (Brazil):

• médica: MEH-djee-kah (the di often sounds like jee in many regions)
• febre: FEH-bree (final e often sounds like ee)

de novo means again. It commonly goes after what it modifies:

• Se eu tiver febre de novo = If I get/have a fever again
  You could move it for emphasis, but this placement is very natural.

Yes.

• de novo = more conversational / everyday
• novamente = a bit more formal or “written” sounding
  Both mean again.

It separates the if-clause from the main clause, which is standard punctuation:

• Se X, Y.
  In informal messages people sometimes skip it, but in standard writing the comma is expected.

Yes. Telefonar is understood everywhere, but ligar is usually more common and casual in Brazil.

• vou ligar para a médica = very natural spoken Brazilian Portuguese
• vou telefonar para a médica = slightly more formal / neutral