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As fever is subsided, it could be a Menstrual cramps
or period pain.
It may be associated with vomiting and nausea.
In every menstrual cycle, an ovum is released from the ovary. if it is not fertilised, then uterus contracts to expel the endometrium ( a inner lining of uterus). This cause the menstrual cramps and pain abdomen.
Nearly more than 50% of women experience menstrual pain
Only few have the identifiable cause.
In some females, menstrual cramps may be associated with medical conditions like endometriosis
, adenomyosis and pelvic inflammatory disease
If she have extreme pain or bothers about pain, You may some investigations like ultrasound abdomen and pelvis, CT, MRI, Hysteroscopy or laparoscopy to rule out above said causes.
If the cause is identified, he need gynaecological assessment and treatment.
Usual initial treatment for menstrual cramps are NSAIDS.
If the pain persists in successive periods, you can try birth control pills and anti prostaglandins
Hope this helps.