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There are many reasons to have severe pain
as it can be due to infection of pelvis;renal or ureteric stone;ovarian cyst
and even extra uterine pregnancy
so first see if you have missed periods and get a urine pregnancy test done to rule out pregnancy.If it is positive then you need to consult a Gynaec and if it is negative please get a ultrasound
done to find the reason and with the reports consult a doctor for treatment.