Learn Hardcore Turkish: Yorgun olunca hep esniyorum.

It’s an adverbial time suffix meaning when/once/whenever. It attaches to verbs: ol- (to be/become) + -unca → olunca. The vowel changes by harmony:

After a back unrounded/front vowels: -ınca/-ince
After a back rounded/front rounded vowels: -unca/-ünce Because the last vowel in ol- is o (back, rounded), you get olunca.

Why use olunca instead of yorgunken or yorgun olduğumda?

Yorgun olunca highlights the moment of becoming tired and what happens then (a trigger/condition feel). It’s very common and colloquial.
Yorgunken means while (I am) tired, focusing on the ongoing state rather than the onset. Also perfectly fine: Yorgunken hep esniyorum.
Yorgun olduğumda is more formal/explicit and often feels a bit more specific: when I am tired. All three are correct; the nuance is onset (olunca) vs state (yorgunken) vs neutral/explicit timing (olduğumda).

Can I say Yorulunca hep esniyorum instead?

Yes. Yorulunca (from yorulmak, to get tired) directly means when I get tired and is very natural. It’s close in meaning to yorgun olunca; some speakers even prefer yorulunca because it directly encodes the “getting tired” event.

Why is it esniyorum and not esnerim?

Both are possible, with a nuance difference:

Esniyorum (present continuous) + hep commonly expresses a general/habitual pattern in everyday speech: Yorgun olunca hep esniyorum.
Esnerim (aorist/simple present) is the textbook habitual: Yorgun olunca hep esnerim. It can sound a bit more general or matter-of-fact. Neither is wrong; choose by tone/register.

What exactly does hep mean here, and how is it different from her zaman, daima, and sürekli?

Hep: very common, informal/neutral; here it means always. It can also mean all in other contexts (e.g., hepimiz = all of us).
Her zaman: literally every time/always, slightly more neutral/formal.
Daima: formal/literary always.
Sürekli: continually/constantly (implies ongoing repetition without much break, not just “always”).

Can I put hep somewhere else in the sentence?

Best is before the verb phrase: Yorgun olunca hep esniyorum.
Other placements:

Hep yorgun olunca esniyorum sounds awkward (as if “always when I’m tired…”).
Yorgun olunca esniyorum hep occurs in casual speech but is less standard. If you want to front it for emphasis, prefer: Hep yorgunken esnerim (still, the original order is most natural here).

Why is it esniyorum and not esneyorum?

In the present continuous, a final a/e in the stem typically raises to ı/i before -yor:

anla- → anlıyorum
bekle- → bekliyorum
esne- → esniyorum So esneyorum is incorrect; esniyorum is the standard form.

Where is the subject I in the sentence?

It’s in the verb ending -um of esniyorum (first-person singular). Turkish usually drops subject pronouns unless you want emphasis: Ben yorgun olunca hep esniyorum stresses “I.” The -ınca clause has no person marking here; its subject defaults to the main clause subject unless you specify otherwise (e.g., Ahmet yorgun olunca ben esniyorum = When Ahmet is tired, I yawn).

Do I need a comma after Yorgun olunca?

It’s optional. Many writers include it for readability when the adverbial clause comes first: Yorgun olunca, hep esniyorum. Without the comma is also common and acceptable.

Why is it olunca and not olınca?

Vowel harmony. The last vowel of ol- is o (back, rounded), so the suffix picks the -unca form: ol- + -unca → olunca. Compare:

gel- + -ince → gelince
gül- + -ünce → gülünce
konuş- + -unca → konuşunca

What are some natural alternative ways to say the same thing?

Yorulunca hep esniyorum.
Yorgunken hep esniyorum.
Yorgun olduğumda hep esniyorum.
Yorgun olduğum zaman hep esniyorum. All are fine; choose by nuance/formality: onset (yorulunca/olunca), state (yorgunken), or more explicit timing (olduğumda/zaman).

How do I say “I don’t always yawn when I’m tired”?

Avoid hep with a negative here. Say:

Yorgun olunca her zaman esnemem. (I don’t always yawn when I’m tired.) For a strong “never”:
Yorgun olunca asla/hiç esnemem.

Any quick pronunciation tips?

c in olunca sounds like English j (as in jam): o-lun-ja.
y in esniyorum is like English y in yes.
The g in yorgun is a hard g.
In verbs with -yor, the stress commonly falls near -yor: esniYOrum.