What Causes Irregular Vaginal Bleeding After A Medical Abortion?

hi,i hav done MTP 40 days back , its 7 weeks pregency, after 15 days i hav done sonography test its almost complete abotion . only 2cm product in side,so again dr given me tab.misoprost200mg 4 tab ,after tat i get bit bleeding for some more days, nw also its bleeding , less n some times no bleeding ,after MTP pills and still nw i hav irregular bleeding, wt is reason? N IS it causes any complications in future? PLZ SUGGEST ME .