I have had sex for last three months every other day and i have missed my period for months, black discharge for two months and spotting ?

Black = old blood: 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.

Limited information: Some of this bleeding and discharge may represent a period. A more detailed record of the pattern would be useful, along with a full exam.