For the past three days, I have been experiencing nausea, diarrhea and a headache. I have had no appetitite, but when I decide to eat anything, I have to go to the bathroom about a half hour later. I am lightheaded at times, feeling drained. Today I thought I was all better and needed to go to work. However, the nausea feeling started and I stayed home again. What could this be? Should I go to a doctor? I have lost about 5 lbs. now.