I am sexually active and i just got off my period wednesday morning and started spotting that night and still are. what is the cause of this?

Irregular bleeding is  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.