The 13th day is generally the day with the highest testosterone levels.
In the week following ovulation, the testosterone level is the lowest and as a result women will experience less interest in sex.
A person who has extremely frequent or a suddenly increased sex drive may be experiencing hypersexuality, while the opposite condition is hyposexuality.
A person may have a desire for sex, but not have the opportunity to act on that desire, or may on personal, moral or religious reasons refrain from acting on the urge.
Freud viewed libido as passing through a series of developmental stages within the individual.