women that have irregular periods, spotting or miss periods

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what was the causes for it? I've had normal regular periods all the time til I gave birth to my daughter. now I have irregular periods, spotting between periods and missed a period. doctor checkrd my hormones everything is normal. I have an ultrasound on June 8th to see what is going on. I'm getting really scared. I'm scared I won't be able to get pregnant anymore.