После долгого лечения челюсть меньше болит, но я всё ещё жую медленно.

Because после always takes the genitive case.

So:

• лечение → nominative
• лечения → genitive singular

The adjective has to match the noun:

• долгое лечение → nominative
• долгого лечения → genitive

So после долгого лечения means after a long treatment / after lengthy treatment.

Челюсть is in the nominative case because it is the grammatical subject of болит.

Russian often says literally:

• Челюсть болит = The jaw hurts
• У меня болит челюсть = My jaw hurts / I have jaw pain

In your sentence, челюсть is the thing that is hurting, so nominative makes sense.

Also note that челюсть is a feminine noun ending in -ь.

Russian often leaves out possessive words like my, your, etc. when the meaning is obvious.

So:

• челюсть болит can naturally mean my jaw hurts if the speaker is talking about themself
• adding моя is possible, but it often sounds more emphatic than necessary

So челюсть меньше болит is perfectly natural.

Меньше here means less.

So:

• болит = hurts / is hurting
• меньше болит = hurts less

Russian often uses a comparative without explicitly saying than before:

• Сейчас меньше болит. = It hurts less now.

You do not need чем раньше unless you want to be explicit.

Usually, меньше is the normal and natural choice here.

• меньше is common in everyday speech
• менее is more formal and often used in bookish or abstract language

So:

• челюсть меньше болит = natural
• челюсть менее болит = unnatural

With verbs like болеть, меньше is the one learners should use.

Both are possible, but всё ещё is stronger and clearer for still.

• ещё can mean still, yet, more, or another
• всё ещё very specifically emphasizes still

So:

• я ещё жую медленно = possible, but a bit less explicit
• я всё ещё жую медленно = I am still chewing slowly

This is a very common expression.

Жую is the 1st person singular present-tense form of жевать = to chew.

Conjugation:

• я жую = I chew / I am chewing
• ты жуёшь
• он / она жуёт
• мы жуём
• вы жуёте
• они жуют

So я всё ещё жую медленно means I still chew slowly / I’m still chewing slowly.

This verb can look surprising because the stem changes from жева- to жу- in the present tense.

Because жевать specifically means to chew, while есть means to eat.

That matters in this sentence: the point is not just that the speaker eats slowly, but that the physical act of chewing is slow, probably because of the jaw.

Compare:

• Я ем медленно. = I eat slowly.
• Я жую медленно. = I chew slowly.

The second one is more precise here.

Yes, word order is flexible.

The neutral order here is:

• я всё ещё жую медленно

But you could also say:

• я всё ещё медленно жую
• медленно я всё ещё жую — more marked, for emphasis

Russian word order often changes to highlight different parts of the sentence, but the original version is very natural.

Because но joins two clauses, and Russian normally puts a comma before it.

Here the two clauses are:

1. После долгого лечения челюсть меньше болит
2. но я всё ещё жую медленно

So the comma is required.

There is not a comma after После долгого лечения, because that opening phrase is just part of the first clause.

They are related, but they mean different things.

• болит = hurts / is painful
• болеет = is ill / is sick

Examples:

• У меня болит челюсть. = My jaw hurts.
• Он болеет. = He is sick.

So in your sentence, болит is correct because the jaw is painful, not “sick.”

A few useful notes:

• всё has ё, so it is pronounced roughly like vsyo
• ещё also has ё, pronounced roughly ye-shCHO
• жую is pronounced roughly zhoo-YOO

Important point: when Russian writes ё, it really matters for pronunciation.

So:

• всё ещё ≈ vsyo ye-shCHO
• жую ≈ zhoo-YOO

Learners often miss ё, especially because it is sometimes written as е in printed text. But in careful learning, it helps to remember the ё sound.

It usually suggests that the speaker is talking about the state after undergoing a long period of treatment, but it does not absolutely force the idea that treatment is 100% finished.

Depending on context, it can mean:

• after a long treatment that is now over
• after a long course of treatment, at this stage

If you wanted to make completion more explicit, Russian could say something like:

• После завершения долгого лечения...
• После долгого курса лечения...

But your original sentence is completely normal and natural.