I had medical abortion 6 months ago and since them my period has been irregular even missed a month. what is the cause?

I suspect hormonal: imbalance since you had medical abortion. Your periods needs to be regulated with hormone pills could be bcp's. See your gyn.

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.