Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
headache [ˈhɛdeɪk] n головна́я боль*f (fig, problem) неприя́тность f
I've got a headache у меня́ боли́т голова́
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.