Welcome to Healthcare magic forum,
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.