What Causes Stomach Upset , Tiredness And Body Pain?

Hi, Since this Thursday around noon,I'v been feeling week, tired, achy, with low appetite and minor upset stomach (no vomiting). I'v spent most of the time sleeping awake only a few hours on Friday sporaticaly. I have no cough, runny nose, sneesing, headache, feever or any other symptoms which I find starnge. Any ideas?