頭が痛いんです。

head; hair (on one's head); mind; brains; intellect; leader; chief; boss; captain; top; tip; beginning; start; head; person; top structural component of a kanji

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

painful; sore; exceeding

yes; yeah; uh huh; negative verb ending used in informal speech (abbr. of negative verb ending "nu"); abbr. of particle "no"; abbr. of particle "ni" (used especially when it precedes the verb "naru")

be; is