عندي ألم في الأسنان اليوم، ولذلك آخذ الدواء الآن.

Arabic often expresses possession with عند + a pronoun suffix.

• عند = at / with / in the possession of
• -ي = me / my

So عندي literally means with me or at me, but in natural English we translate it as I have.

So:

• عندي ألم = I have pain

This is a very common Arabic structure.

Because Arabic does not always use a verb the way English does.

In عندي ألم:

• عندي already gives the idea of I have
• ألم is the thing possessed

So Arabic does not need a separate verb like have here.

This is normal in Arabic, not an omission.

After expressions like عندي or لدي, the noun is very often indefinite when you are introducing something that exists or that someone has.

So:

• عندي ألم = I have a pain / pain
• عندي كتاب = I have a book

If you said عندي الألم, it would usually sound much less natural unless you were referring to some specific, already-known pain.

So the indefinite ألم is the normal choice here.

There are two useful points here.

1. Arabic often uses the definite article with body parts When the owner is obvious from context, Arabic frequently says the body part rather than my body part.

So في الأسنان can naturally mean in the teeth, with the meaning understood as in my teeth from the sentence.

2. The plural is natural here Arabic often talks about this kind of pain using teeth as a set or area:

• ألم في الأسنان = pain in the teeth / toothache

If you wanted to mention only one tooth, you could say something like:

• ألم في سنّ
• ألم في أحد أسناني

Yes. Both are possible, but they are structured differently.

• ألم في الأسنان = pain in the teeth
• ألم الأسنان = tooth pain / pain of the teeth

The sentence you were given uses the prepositional phrase في الأسنان to show location. That is perfectly correct and clear.

Yes, اليوم is flexible.

In your sentence, it comes after في الأسنان:

• عندي ألم في الأسنان اليوم

That sounds natural and means I have tooth pain today.

But Arabic often allows adverbs of time to move around, for example:

• اليوم عندي ألم في الأسنان
• عندي اليوم ألم في الأسنان

These are all understandable. The original sentence has a neutral, natural word order.

ولذلك means and therefore, and so, or for that reason.

It is made up of:

• و = and
• لِـ = for / because of
• ذلك = that

So literally it is something like and for that or and for that reason.

It is a common connector in Modern Standard Arabic, especially in writing and careful speech.

Because آخذ is present tense, while أخذ is usually past tense.

• أخذ = he took
• آخذ = I take / I am taking

The verb root is أخذ. In the first-person present, the form is historically أأخذ. Because two hamzas come together, Arabic writes this as آخذ with alif madda.

So in this sentence:

• آخذ الدواء الآن = I am taking the medicine now

Because the verb itself already shows the subject.

آخذ already means I take / I am taking, so أنا is not necessary.

You could add أنا for emphasis:

• أنا آخذ الدواء الآن

But without emphasis, Arabic usually leaves the subject pronoun out because it is already built into the verb form.

A careful MSA pronunciation is approximately:

• آخذ = ʾā-khu-dhu

You can think of it as:

• a long ā
• then kh
• then dh as in the th of this

In fully vowelled MSA, it is آخُذُ.

Because the speaker is referring to a specific medicine, or to medicine that is understood from the situation.

So:

• آخذ الدواء = I am taking the medicine

This is very natural when the medicine is known or contextually obvious.

If you wanted to say I am taking some medicine, you could use an indefinite form such as:

• آخذ دواءً

But الدواء is very natural in the original sentence.

آخذ الدواء is grammatical and understandable.

However, in MSA, many speakers and writers also use:

• أتناول الدواء

This often sounds a bit more specifically like take medicine.

So both are possible:

• آخذ الدواء الآن = perfectly fine
• أتناول الدواء الآن = also very common and natural

Yes.

• لدي ألم في الأسنان اليوم
• عندي ألم في الأسنان اليوم

Both mean the same thing here.

A useful general difference is:

• عندي = very common, natural, everyday
• لدي = often a bit more formal or written

In Modern Standard Arabic, both are acceptable.

In very careful, fully vowelled MSA, the sentence would be read something like:

• عندي ألمٌ في الأسنانِ اليومَ، ولذلك آخذُ الدواءَ الآنَ.

But in normal spoken MSA, many speakers do not pronounce all final case endings clearly.

So in practice, learners often hear something closer to:

• عندي ألم في الأسنان اليوم، ولذلك آخذ الدواء الآن

Both are useful to know:

• with endings for formal grammar and reading
• without endings for normal real-life pronunciation

Although it is written الدواء, it is pronounced with assimilation because د is a sun letter.

So the l sound of الـ is not pronounced clearly. Instead, you get:

• الدواء → approximately ad-dawāʾ

Also notice the final hamza at the end of the word.

So in careful pronunciation:

• آخذ الدواء ≈ ʾākhudhu d-dawāʾa