Πρέπει να πάρω τη βιταμίνη μου μετά το πρωινό.

Because after πρέπει in this meaning, Greek normally uses να + a verb form that expresses a single, complete action.

• να πάρω = that I take / for me to take in the sense of take it once, as a complete act
• παίρνω = I take / I am taking / I usually take

Here, the idea is I need to take my vitamin after breakfast, so Greek uses να πάρω.

Also, πάρω is the aorist subjunctive form of παίρνω.

Πρέπει means must, have to, or need to.

It is an impersonal verb, so it does not change according to the person:

• Πρέπει να φύγω = I have to leave
• Πρέπει να φύγεις = You have to leave
• Πρέπει να φύγουμε = We have to leave

So in this sentence:

• Πρέπει να πάρω... = I have to take...

Greek does not need a separate word for I here, because the verb form already shows the person.

This is because παίρνω has a different stem in the aorist.

• Present stem: παίρν-
• Aorist stem: παρ-

So:

• παίρνω = I take
• να πάρω = to take / that I take as a single completed action
• πήρα = I took

This kind of stem change is common in Greek and just has to be learned as part of the verb.

Τη is the feminine singular definite article in the accusative case, meaning the.

The noun βιταμίνη is the direct object of πάρω, so it appears with the accusative article:

• Nominative: η βιταμίνη
• Accusative: τη(ν) βιταμίνη

So:

• τη βιταμίνη = the vitamin

In this sentence, it is further specified by μου, so the full phrase means my vitamin.

In Greek, possessive pronouns like μου often come after the noun.

So:

• η βιταμίνη μου = my vitamin
• literally: the vitamin my

This is the normal Greek pattern.

You can think of μου here as a weak possessive form meaning my.

Greek often uses the definite article with possessed nouns, much more than English does.

So Greek prefers:

• τη βιταμίνη μου = my vitamin

rather than leaving the article out.

This is very normal:

• το σπίτι μου = my house
• η μητέρα μου = my mother
• τα βιβλία μου = my books

So the article is not optional in most ordinary cases like this.

Because Greek usually leaves out subject pronouns when they are not needed.

The verb form πάρω already shows first person singular, so I is understood.

• Πρέπει να πάρω = I have to take
• Πρέπει να πάρεις = you have to take
• Πρέπει να πάρει = he/she/it has to take

You could add εγώ for emphasis, but normally you would not:

• Εγώ πρέπει να πάρω τη βιταμίνη μου... = I have to take my vitamin... with extra emphasis on I

It means after breakfast.

• μετά = after
• το πρωινό = breakfast

So:

• μετά το πρωινό = after breakfast

In Modern Greek, μετά is followed by the accusative in this meaning.

Not here.

Πρωινό can be related to morning, but as a noun it commonly means breakfast.

Examples:

• το πρωί = the morning / in the morning
• το πρωινό = breakfast
• πρωινός, πρωινή, πρωινό = morning, early, or morning-related as an adjective depending on context

So in this sentence, το πρωινό definitely means breakfast.

Both are possible.

The full form is την, but before many consonants in everyday speech and writing, the final -ν is often dropped:

• την βιταμίνη
• τη βιταμίνη

Both mean the same thing.

In standard usage, keeping or dropping the final -ν depends partly on the sound that follows and partly on style. Before β, many speakers and writers drop it, so τη βιταμίνη is very natural.

Yes, that is also possible.

You may hear:

• μετά το πρωινό
• μετά από το πρωινό

Both mean after breakfast.

Very often, Greek simply uses μετά + accusative without από, especially in straightforward expressions like this.

So the version in the sentence is perfectly normal and natural.

Yes, βιταμίνη is a feminine noun.

Its basic forms are:

• Nominative: η βιταμίνη
• Accusative: τη(ν) βιταμίνη
• Genitive: της βιταμίνης

That is why the article is feminine: τη.

It can often suggest a general instruction or routine, but grammatically the form να πάρω focuses on the action as a whole, not on repeated ongoing action.

So depending on context, it could mean:

• I need to take my vitamin after breakfast as a general habit or instruction
• I need to take my vitamin after breakfast today in a specific situation

Greek does not always mark that distinction as sharply as English does here; context tells you which meaning is intended.