No appetite all day??

I've had no appetite all day. I don't think I'm sick or anything but I'm just not hungry. I had it last night a bit too. I feel fine otherwise but just don't feel like eating, I had to force myself to eat my breakfast and some crackers for lunch. I've been extremely stressed lately so maybe it could be that, or I was supposed to get my period today (I haven't yet) so maybe it could be that too. Should I be worried?