Does Isotretinoin stop you from getting your period monthly?

I recently started being on this medicine called Isotretinoin, and the first few weeks I had the side effects; rash, dry lips, dry face and etc... But I'm suppose to get my period around between 23-25th.. And it's the 29 & I still haven't got my period.. I'm a bit scared!! It's almost the end of the month and I haven't got my period.. Do you think that medication steps you from getting your period?