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Have you confirmed pregnancy
by Urine pregnancy test. According to ultrasound
there is no pregnancy and you are having menstruation
signs. The uterus will contract sometimes especially during menses in an attempt to remove fibroid which is a muscular swelling inside the uterus. That's what you must be feeling as movements. There can be more pain in menses time for which you may need pain killers. Better to go for fibroid removal
by surgery if much problems.