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U have missed ur periods for 12 days may be due to less hemoglobin
or severe stress
, u had severe pain abdomen
to intiate ur periods, since ur urine test and scanning was normal so ur doctor started norethisterone
for 5 days, after stopping the tablets bleeding started, its called withdrawl bleeding which happens when u stop the tablet.
There is nothing to worry, its a normal process.
Hope I have answered ur question.