Ieri avevo mal di stomaco e un po’ di nausea dopo cena.

Avevo is the imperfetto of avere, and it is often used for a past state or condition: how someone felt, what the situation was, what was going on in the background.

So Ieri avevo mal di stomaco... sounds like Yesterday I had a stomachache... / I was feeling sick...

If you said ho avuto, that would sound more like a completed event, often with a clearer beginning/end or as a single fact:

• Ieri ho avuto mal di stomaco per due ore.
• Dopo cena ho avuto un attacco di nausea.

In this sentence, avevo is natural because it describes how the speaker was feeling.

Mal di stomaco is a very common expression meaning stomachache or stomach pain.

Literally, it is something like pain of stomach, but you should learn it as a fixed expression:

• avere mal di stomaco = to have a stomachache

Similar expressions are:

• mal di testa = headache
• mal di schiena = backache
• mal di denti = toothache

So avevo mal di stomaco is the normal way to say I had a stomachache.

Because mal di stomaco works as a set expression. In Italian, many body-pain expressions do not use an article:

• ho mal di testa
• ha mal di gola
• avevamo mal di schiena

English often uses a in these cases, but Italian usually does not.

So:

• I had a stomachache → Avevo mal di stomaco not normally Avevo un mal di stomaco

Un po’ di means a little or a bit of.

In the sentence:

• un po’ di nausea = a little nausea / some nausea

This is a very common pattern:

• un po’ di fame = a little hunger
• un po’ di tempo = a little time
• un po’ di acqua = a little water

It is used before nouns, especially uncountable ones.

Because po’ is a shortened form of poco.

So:

• un poco di and un po’ di mean the same thing

The apostrophe shows that the word has been shortened. This is the correct spelling:

• un po’

Not:

• un pò

Because un po’ is normally followed by di before a noun.

So:

• un po’ di nausea
• un po’ di pane
• un po’ di fortuna

You would not normally say:

• un po’ nausea

The di is part of the structure.

Yes, you can. Avere nausea is a normal expression in Italian.

The difference is mainly in nuance:

• avevo nausea = I felt nauseous / I had nausea
• avevo un po’ di nausea = I had a little nausea

The version with un po’ di sounds softer and more specific. It suggests the nausea was present, but not necessarily severe.

In Italian, meals often appear without an article after prepositions when speaking generally:

• a colazione = at breakfast
• prima di pranzo = before lunch
• dopo cena = after dinner

So dopo cena is a very natural way to say after dinner.

You may hear dopo la cena too, but that usually sounds more specific, as if referring to a particular dinner or emphasizing the meal itself.

Yes. Italian word order is flexible.

The original sentence:

• Ieri avevo mal di stomaco e un po’ di nausea dopo cena.

Other natural possibilities include:

• Dopo cena ieri avevo mal di stomaco e un po’ di nausea.
• Avevo mal di stomaco e un po’ di nausea dopo cena, ieri.
• Ieri, dopo cena, avevo mal di stomaco e un po’ di nausea.

The original version is very natural, but Italian often moves time expressions around for emphasis or style.

No. Ieri can appear in different places:

• Ieri avevo mal di stomaco...
• Avevo mal di stomaco ieri...
• Dopo cena ieri avevo...

Putting ieri first is very common because it sets the time immediately. It is often the most neutral choice.

Stomaco is more specific and refers to the stomach.
Pancia is more general and often means belly or tummy.

So:

• mal di stomaco = stomachache, stomach pain
• mal di pancia = tummy ache / belly ache

Both are common, but mal di pancia can sound slightly less technical and sometimes a bit more everyday or child-directed, depending on context.

Not with mal di stomaco.

You say:

• avevo mal di stomaco
• avevo nausea

If you want to use ero, you need an adjective instead:

• ero malato/a = I was ill
• ero nauseato/a = I was nauseous

So ero mal di stomaco would be incorrect.