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There are various causes of abortion.
Maternal causes are anemia ,diabetes , hypothyroidism , hypertension , Rh incompatibility, syphilis etc
Fetal causes can be infections like toxoplasmosis , rubella , herpes , cytomegalovirus etc
Other causes can be uterine factors like septate uterus , bicornuate uterus
, incompetent Os and progesterone deficiency
I hope you have got all the investigations done like Hb , ABO and Rh , blood sugar F , Torch test , Anticardiolipin antibody test , VDRL , Thyroid profile etc.
As you said you passed the whole fetus and there is only blood collection in the cavity so it is a complete abortion.
The most common cause for body aches can be anemia due to bleeding.
It can be due to calcium deficiency
Take iron and calcium supplements
and diet rich in iron and calcium.
For stomach pain take antispasmodics under your doctor's guidance and prescription.
With good diet , proper rest , no stress , good antibiotics , haemostatics , iron , calcium and pain killers these symptoms will resolve very soon.
Remain under guidance of your OBGYN
for further follow ups.