Falamos sobre sexo com o médico.

Portuguese often omits subject pronouns when the verb ending already shows who the subject is.

• Falamos = we speak / we talked
• So nós is optional here.

You could also say:

• Nós falamos sobre sexo com o médico.

That sounds fine too, but adding nós usually gives emphasis, contrast, or extra clarity.

It can mean either one, depending on context.

For -ar verbs like falar, the present and the preterite forms for nós are spelled the same:

• falamos = we speak / we talk
• falamos = we spoke / we talked

So this sentence by itself is ambiguous.

Context usually makes it clear:

• Agora falamos sobre sexo com o médico. = Now we’re talking about sex with the doctor.
• Ontem falamos sobre sexo com o médico. = Yesterday we talked about sex with the doctor.

In everyday Brazilian Portuguese, people often use a gente fala or a gente falou to avoid this ambiguity.

Because falar sobre means to talk about.

So:

• falamos sobre sexo = we talked about sex

This is very natural Portuguese.

You may also hear:

• falar de sexo

That also means to talk about sex. In many cases, sobre and de are both possible, though sobre can sound a bit more explicitly about the topic.

Because sexo is being used in a general sense.

In Portuguese, abstract or general nouns often appear without an article, especially after expressions like falar sobre or falar de:

• falar sobre sexo
• falar de política
• falar sobre dinheiro

Adding an article is sometimes possible, but it can sound more specific, marked, or just less neutral depending on context.

So sobre sexo is the most natural general phrasing here.

The natural reading is:

• Falamos ... com o médico = We talked ... with the doctor

So com o médico tells you who we talked with.

It does not normally mean about the doctor.

If you wanted to say We talked about the doctor’s sex, you would need something like:

• Falamos sobre o sexo do médico.

That is a very different structure.

Because Portuguese often uses the definite article when referring to a specific person already understood in context.

• com o médico = with the doctor
• com um médico = with a doctor

So o suggests a particular doctor.

Also, note that:

• com + o stays com o

Unlike some other prepositions, it does not contract into one word here.

For example:

• de + o = do
• em + o = no
• but com + o = com o

Yes. That is also correct and very natural.

Both of these work:

• Falamos sobre sexo com o médico.
• Falamos com o médico sobre sexo.

The meaning is basically the same. The difference is mostly word order and focus:

• sobre sexo first: emphasizes the topic
• com o médico first: emphasizes who you spoke with

Portuguese allows this kind of flexibility.

In this sentence, the most natural meaning is sex as a topic related to sexuality / sexual relations.

The word sexo can also mean biological sex in other contexts, for example on forms:

• Sexo: masculino / feminino

But if someone wants to talk about gender in the social or identity sense, modern Brazilian Portuguese often uses:

• gênero

So in falar sobre sexo, most people will understand it as talking about sex.

You would say:

• Falamos sobre sexo com a médica.

Changes:

• o médico → a médica

So the article and the noun both change to the feminine form.

Yes, it is natural.

It sounds like a normal sentence you might say in a medical or personal context. Depending on style and context, Brazilians might also say things like:

• A gente falou sobre sexo com o médico.
• Conversamos sobre sexo com o médico.

These are also natural, but your original sentence is perfectly good Portuguese.