Abnormal period

So for the whole month of January I had no period at all went to the doctor everything came back negative ... So then on Thursday I wake up to a "period" only cramping for maybe 2 hours then it completely stopped like I had taken medication and on top of that it was lighter than normal I'd only have to use maybe 2 tampons if that a day The only thing is it normally comes like clockwork at the end of every month and last for 5-6 days and this only lasted 3 days I haven't been really stressed lately but I've been extra tired durning the day any suggestions