Ontem tive uma picada de mosquito no braço e fiquei com muita comichão.

Tive is the 1st person singular preterite of ter.

Here it means I had/got in a completed past event:

• Ontem tive uma picada... = yesterday, this happened.

A learner might expect tinha, but tinha usually suggests:

• an ongoing past state,
• background information,
• or repeated past situations.

So:

• Ontem tive uma picada de mosquito = one specific event yesterday.
• Quando era criança, tinha muitas picadas de mosquito no verão = repeated situation in the past.

In European Portuguese, ter is very commonly used where English might say to have or to get.

So:

• tive uma picada literally = I had a bite
• but in natural English, the idea is often I got a bite

Portuguese often keeps ter in this kind of situation:

• ter uma dor = to have a pain
• ter febre = to have a fever
• ter uma reação = to have a reaction

So tive uma picada de mosquito is a very normal way to express that experience.

Picada is the noun bite or sting, depending on the animal/insect.

So:

• uma picada de mosquito = a mosquito bite

Literally, it is:

• picada = bite/sting
• de mosquito = of mosquito / from a mosquito

This is a very common Portuguese pattern:

• picada de abelha = bee sting
• mordida de cão = dog bite

Portuguese does not normally build noun+noun compounds the same way English does.

English:

• mosquito bite
• summer holiday
• chicken soup

Portuguese usually uses de:

• picada de mosquito
• férias de verão
• sopa de frango

So de mosquito is the normal way to say what kind of bite it was.

No is a contraction:

• em + o = no

So:

• no braço = in/on the arm

With body parts, Portuguese very often uses the definite article:

• na cabeça
• no braço
• na perna

That is why you do not say just em braço.

Portuguese often uses the definite article with body parts where English uses a possessive like my, your, etc.

So Portuguese prefers:

• no braço = on the arm

Even though in English we usually say:

• on my arm

The owner is already understood from the context:

• tive uma picada... no braço clearly means it was on my arm.

This is a very common pattern:

• Doe-me a cabeça = My head hurts
• Lavei as mãos = I washed my hands

Fiquei is the preterite of ficar, which often means to become, to be left, or to end up in a state.

So:

• fiquei com muita comichão = I ended up with a lot of itching / it became very itchy for me

This structure is very common:

• ficar com fome = to become hungry
• ficar com sono = to become sleepy
• ficar com medo = to become afraid

It often describes the resulting state after something happens.

You can say tive muita comichão, and it would be understandable.

But fiquei com muita comichão often sounds more natural here because it highlights the change of state:

• first the mosquito bit me,
• then I ended up feeling itchy.

So there is a sequence:

1. tive uma picada de mosquito
2. fiquei com muita comichão

That makes ficar com a very good choice.

Comichão means itchiness or itching.

In European Portuguese, comichão is the standard everyday word.

In Brazilian Portuguese, learners will often hear:

• coceira

So:

• Portugal: Tenho comichão
• Brazil: Estou com coceira / Tenho coceira

If you are learning Portuguese from Portugal, comichão is absolutely the word to learn.

Here comichão is being treated as an uncountable noun, like itchiness in English.

So:

• muita comichão = a lot of itching

This is the normal way to say it.

You would not usually count separate itches here. You are talking about the sensation in general, so the singular is used:

• muita comichão
• pouca comichão

Because muita is already acting as the determiner here.

Compare:

• a comichão = the itchiness
• muita comichão = a lot of itchiness

Just as in English you say a lot of itching, not the a lot of itching, Portuguese does not add an article here.

Yes, e fiquei literally means and I became / and I ended up.

Portuguese often drops subject pronouns when the verb ending already makes the subject clear.

So:

• tive clearly shows I
• fiquei also clearly shows I

That is why eu is unnecessary here.

You could say:

• Ontem eu tive... e fiquei...

But it is usually more natural to leave eu out unless you want emphasis or contrast.

Putting ontem first is very natural because it sets the time frame straight away.

Portuguese allows flexibility here:

• Ontem tive uma picada de mosquito...
• Tive uma picada de mosquito ontem...

Both are correct. Starting with ontem is common when the speaker wants to frame the whole sentence as something that happened yesterday.

Sometimes yes, because picadela can also mean bite/sting.

However, picada de mosquito is a very common and safe choice. For a learner, it is the more neutral and broadly useful option.

So if you want the most standard expression:

• uma picada de mosquito

It means specifically mosquito.

It does not generally mean just any bug or insect.

So:

• mosquito = mosquito
• inseto = insect
• bicho = bug/animal/creature, depending on context

If the sentence says picada de mosquito, it is specifically a mosquito bite.

Yes, it sounds natural in European Portuguese.

A few natural alternatives would be:

• Ontem um mosquito picou-me no braço e fiquei com muita comichão.
• Ontem levei uma picada de mosquito no braço e fiquei com muita comichão.

But the original sentence is perfectly normal and useful because it uses common everyday structures:

• ter uma picada
• ficar com comichão

So it is a very good sentence to learn from.