What could this mean?

Hi, I AMA 15 year old girl. I have had diarrhea for about 5 days. I have had slight cramps but they only last for a few minutes at a time. I am eating what I normally eat, and I had a slight fever 99.2 on Monday (the first day of the symptoms). I had a nauseas feeling, but never threw up. I've had jeadaches more than usual as well. Also, last year, around October, everything I ate would make me feel nauseas. Every morning I would get diarrhea. But that went away by Christmas time and before it stopped, it didn't happen as frequently. I'm really scared. What should I do and what is causing this? Please help. I'm really scared