What Causes Diarrhea, Stomach Rumbling And Headache?

I am a 71 year old female experiencing diahhrea for over a week - symptoms are - each morning experiencing loose runnybowel movement - Rumbling in stomach in wee early hours that wakes me up - then finally having the diahhrea - feel fine then for most of the rest of the day - until later in day - I develope a headache and chills - plus stomach feels sick - I also become irritable and very exhausted - so tired - cannot keep my eyes open- becoming more irritable- was just at my scheduled doctor appt on Tuesday- the 8th and all blood work was excellent - doctor was told at that time that I must have a stomach virus - but it is going on now too long - any ideas what is my problem??