Any advice ? Someone who has been through this !

Well I just started crossfit two weeks ago and I am eating healthy again and working out intensely there. I was suppose to get my period two weeks ago and before anyone says "ughhh take a prego test " I already did and I just took one again fifteen minutes ago and it is negative . My concern is could it possibly be the prego test I got (first response ) or could be from working out . I just am a little nervous never skipped a period !