My wife has got her period a week and half early and she only bleeds throughout the day. it goes away at night. what can it be?

Multiple factors: Other medication can interfere with the birth control. The medication it self can cause this as well. She should see her physician to rule out infections or other causes.

Irregular periods: Irregular periods are one of the most common problems obgyns treat. If this is one time problem it usually resolves on its own. If this is a recurring problem you should be evaluated. Infections ; hormonal changes can cause spotting. If there is a concern for pregnancy then do a home pregnancy test . There are many options available to help regulate the menstrual cycle. Schedule a visit.