Got first period 3mnths after medical abortion. first bled and blood clots now at night nothing comes out and then it starts up during the day, why?

Post abortion: A "medical abortion" may not always result in complete expulsion of all pregnancy tissue. A delay of your menses for "three months" is uncommon, but at this point you may require a "dilation and currettage: D&C" to remove the remaining tissue, so your cycles are again regular. You should obtain a serum pregnancy test in case you may be (again) pregnant.