Learn Spanish (Latin America): ¿Te duele la cabeza por leer los subtítulos? - Does your head hurt from reading the subtitles?

Doler (to hurt/ache) works exactly like gustar. The person feeling the pain is shown by the pronoun te (to you), but the grammatical subject is actually the thing that hurts. Since la cabeza (the head) is singular, the verb takes the singular "it" form: duele.

Why does it say la cabeza (the head) instead of tu cabeza (your head)?

In Spanish, when talking about body parts, you almost always use the definite article (el, la, los, las) rather than a possessive word like tu (your). The pronoun te earlier in the sentence already makes it clear whose head is hurting.

The English translation says "reading", so why is it leer instead of the "-ing" form (leyendo)?

In English, we often use "-ing" words after prepositions (like "from reading"). But in Spanish, whenever a verb comes immediately after a preposition like por, it must always be in its infinitive (unconjugated) form, which is leer here.

Why do we use por here instead of para?