My period came on jan12/2013 ended on jan.15 when do i ovulate cycle n last 5month.cyle length26, 24, 25, 28, 28?

Easy: You would have ovulated 14 days before each of your periods started. Virtually every woman will start the period 14 days after ovulation, unless she conceives. The variation in cycle length results from variation in the time from the beginning of the period until ovulation does occur - that can vary from 7 days to 21 days giving total cycle lengths of 21 to 36 days.