Why Am I Having Repeated Abortions After Having 3 Kids ?

HI I am trying to conceive , Ihad 4 repeated abortion in the last 3 years &i do all immunological tests & there are rhaumatiod factor positive & and antimicrosomal antibodies positive&but i donot have any signs of rhaumatoid or thyroid illness &please tell me the treatment of recurrent abortion?what are the treatmment?age38 years I have 3 childs & hieght162 &w 65 kg & abortion every time after2 or 2 and half months& the 4 recurrent abortion occur after ihave frist 3 childs&what are the treatment for me? anticardiolipen and lupus are negative&Itake difuston ,asprin andfolic in the previous 2 abortion.