Seriously Confused

Serious answers only please. 
I am late for my period. I was supposed to start on the first and it is now the fourth. I took a over the counter test last night and it was negative and one again this morning which was negative. 
I'm not TTC, but I have no signs of my period. I've been overly tired and a little bloated but nothing too horrible. I was feeling nauseous last night and all this morning with lose stool but now I think it might have been the flu. 
My question is when should I test again? And I know nobody is a doctor here but does it sound like pregnancy or just a late cycle?