Suggest Remedy For Missed Periods

i didnt have my period for over 3 months, i went to the dr. i know im not pregnant, so my dr put me on aygestin. i have been taking it for 3 days now. i have been having really bad cramps, moody, just all around in a bad mood. i was wondering if the cramps are normal, and how long after i take it will i get my period? will i be able to have more children?