No me pongo el pijama hasta que termine de ducharme.

Because the verb here is ponerse, not just poner.

• poner = to put / to place
• ponerse = to put on oneself

With clothes, Spanish very often uses the reflexive form, because you are putting the item on your own body. So:

• Pongo el libro en la mesa = I put the book on the table
• Me pongo el pijama = I put on my pyjamas

So the me is not optional here; it is part of the meaning.

In Spanish, no goes before the whole verb phrase, and object/reflexive pronouns like me usually go right before the conjugated verb.

So the normal order is:

• No + pronoun + verb
• No me pongo

Not:

• me no pongo ❌

You will see this pattern constantly:

• No me levanto temprano
• No te entiendo
• No se ducha por la noche

Spanish often leaves out subject pronouns because the verb ending already shows who the subject is.

• pongo already means I put on
• so yo is unnecessary unless you want emphasis or contrast

Compare:

• No me pongo el pijama... = neutral, normal
• Yo no me pongo el pijama... = more emphatic, maybe contrasting with someone else

For example:

• Él se pone el pijama antes, pero yo no me pongo el pijama hasta que termine de ducharme.

Spanish often uses the definite article with clothing, especially with reflexive verbs like ponerse.

So Spanish prefers:

• Me pongo el pijama
• Se quitó la chaqueta
• Nos lavamos las manos

rather than always saying mi, su, mis, etc.

It still means my pyjamas here because the reflexive structure already makes that clear.

As for pijama, in Spanish it is normally singular: el pijama. English often uses the plural pyjamas, but Spanish treats it as one item of clothing.

The present tense in Spanish is often used for habits, routines, and general truths.

So No me pongo el pijama hasta que termine de ducharme can mean something like a regular rule or routine: this is what I do.

That is similar to English:

• I don’t go to bed before I brush my teeth
• I don’t put on my pyjamas until I finish showering

If you wanted to talk about one specific future occasion, Spanish could also use the future:

• No me pondré el pijama hasta que termine de ducharme

But the present is completely natural for a habit or usual sequence.

Because after hasta que, Spanish uses the subjunctive when the action is still pending, expected, or in the future relative to the main verb.

Here, the finishing of the shower has not happened yet at the point being described, so Spanish uses the subjunctive:

• hasta que termine

not:

• hasta que termino ❌

A useful rule:

• hasta que + subjunctive = until something happens later / has not happened yet
• hasta que + indicative = until something that did happen / happens as a fact in a past context

Examples:

• No salgo hasta que llegue Ana.
• Esperé hasta que llegó Ana.

Also, the subjunctive here is not caused by the no. It is caused by hasta que plus a non-completed action.

Because terminar de + infinitive is the normal structure for to finish doing something.

So:

• terminar de ducharme = to finish showering
• terminar de comer = to finish eating
• terminar de estudiar = to finish studying

Without de, it would not be the normal construction in this sentence.

Be careful not to confuse this with acabar de + infinitive, which usually means to have just done something:

• Acabo de ducharme = I have just showered

That is different from termino de ducharme, which means I finish showering.

Because with an infinitive, reflexive pronouns attach to the end of the verb.

So:

• ducharme
• lavarte
• vestirse

That is the normal pattern.

Compare:

• Me ducho = conjugated verb, pronoun goes before
• Quiero ducharme = infinitive, pronoun attaches to the end
• Termine de ducharme = same idea

This sentence has two instances of me, but they belong to two different verbs:

• me pongo
• ducharme

Both refer to the same person, but each one is part of its own verb structure.

Yes, ducharse is the normal verb for to shower oneself / to take a shower.

• Me ducho por la mañana = I shower in the morning

Without the reflexive pronoun, duchar is usually transitive, meaning you shower someone else:

• Duché al niño = I showered the child

So in your sentence, ducharme is the natural choice because the speaker is the one taking the shower.

Yes. That is also correct.

When the subject is the same for both actions, Spanish can often use an infinitive instead of hasta que + subjunctive:

• No me pongo el pijama hasta que termine de ducharme
• No me pongo el pijama hasta terminar de ducharme

Both are natural. The version with hasta que termine feels more like a full clause; the infinitive version is a bit more compact.

Learners often meet the hasta que + subjunctive pattern first because it clearly shows the grammar of until with a pending action.